Rough idle - smooths out when I drive (going insane) Options

[97Supra]

I have never found a problem with an engine that I was unable to fix with some moderate thinking.. but with this 1.8L engine I have done the following:

Symptoms:

Car starts VERY FAST. Click vroom. Perfect. Idles 1200 or so to warm up, then drops to what appears to be factory setting around 750 or so. In park, or neutral the engine is vibrating but you don't feel it as bad. The moment you put it in a gear, R or D the entire car shakes to pieces. Touch the gas, and with a load the problem is magically gone until the next stop light... it never stalls. I just failed emissions for HC.. (unburned fuel... which made me think ignition system)


- plugs
- cap
- rotor
- wires
- coolant temp sensor
- egr check
- re-ground everything
- iac clean / check
- vacuum sensor check
- replace all vacuum lines
- checked for leaks anywhere
- set base timing to factory specs
- changed fluids
- changed motor mounts
- unplugged and plugged back in every sensor to no avail
- put on an entirely different distributor
- drained the gas tank and put in all new fuel

.. The only thing I can think of that I did not try is replacing the ignition coil in the distributor, it could be bad.. but the likely hood of both the old and newer distributors coils both being bad is probably slim... I'm going insane.

Now after messing with the TPS my idle wont go below 1,000 or so.. guess I put it back in the wrong position. Oh well, I'll figure that out later but is there anything I'm missing here? I've tried everything I searched google many times I can't even find anything else to check.

fuel pressure? Any ideas....

This post has been edited by 97Supra: Mar 1, 2011 - 7:05 PM

[Smaay]

hhmmm got me stumped, messing with your TPS is bad. it throws off the calibration. did you change the front and rear motor mounts. its usually the rear that causes the vibrations.

[97Supra]

yes, all mounts changed. Gotta find the route cause of the crappy combustion that's causing the shake, because it made me fail emissions.

I just went to pull my pcv valve to see if it's operational and i broke it in half it was so brittle... haha i guess i won't know if it was the problem until tomorrow when I go buy a new one.... stupid small thing.. I hope that's the problem but I don't think it will be

This post has been edited by 97Supra: Mar 1, 2011 - 9:21 PM

[97Supra]

installed an entirely different rail / fpr / injectors... installed entirely different throttle body and iac valve... installed other unknown sensors on firewall... still nothing yet same crappy rough idle.. still waiting on the ignition coil to arrive hopefully today.

compression is 200 190 195 195.. don't see a problem there

[RavenAegis45]

Did you check your alternators output it may be old and putting out lower than what's needed

[d3ath2009]

my brother's civic had basically the same problem. we put new plugs and wires, dizzy and button and it had no probs. eventually needed a new coil pack so u may wanna look into that too

[97Supra]

alternator is brand new 14-15+v running

just installed coil pack 15 mins ago, still shaking like a SOB lol

I'm starting to think it's the EGR valve I thought it was working properly but I ordered a new one just to be sure. dang those stupid things are expensive.... $203 shipped for the EGR @ rockauto

I'll post back when I put the EGR in when it arrives to see if anything has changed!

What a tricky tricky problem...

From research I've done online it looks like egr valves can act like a vacuum leak causing a rough idle / misfire / lean running condition at idle and that would explain why the emissions are perfect anything above idle but only HC is high at idle. I hope i hope i hope... if it's not the EGR I'm just going to either replace the head, or the entire engine although I just put this engine in the car about month ago.

[97Supra]

I installed the new ERG today and that was a waste of $200 bucks... That didn't help anything. I then made a new negative battery cable, and grounded it in 2 places, that didn't help either.. the list is growing.

Getting back to the alternator theory, I grabbed my multi meter and at warm idle on the battery im reading way low around 12.4 or 12.5. off idle it's around 14.4 but it differs it's either one or the other all the time it fluctuates which is leading me to believe it's either faulty wiring to / from the alternator, or the alternator itself. If I wiggle the plug on the exhaust side of the alternator the car trys to stall.. it appears to be somewhat melted visually. I guess a good LOOKING alternator can still be a piece of junk.. perhaps

Anybody have any experience with such a thing? Is it going to be wiring, or the alternator? I'll try to figure it out tomorrow it's dark and cold.. till next time

This post has been edited by 97Supra: Mar 7, 2011 - 7:04 PM

[cyberblader1130]

Any exhaust leaks? O2 sensors good? Have you checked your catalytic converter at all?

As for the Alt, clean all connects, maybe replace any worn wiring?

If the you suspect the alt isn't up to specs, take it to a local shop and ask for an Alt. test. They should be happy to test it and let you know if it's the cause or not.

This post has been edited by cyberblader1130: Mar 7, 2011 - 7:33 PM

[97Supra]

New header / had to have a shop cut it at the flex and make it fit the car, ebay sent me the wrong one.. haha 02 sensors are new/er and a new catalytic converter was just installed about a month ago at meineke.

I'm gonna take your advice and order a new pigtail plug for the alternator since wiggling it makes the car die.. obviously the plug is screwed, but the low voltage output from the alt.. I will go get a new alt. tomorrow morning and install it. if it helps I will be very glad.. this cars been through a lot!

[cyberblader1130]

New header / had to have a shop cut it at the flex and make it fit the car, ebay sent me the wrong one.. haha 02 sensors are new/er and a new catalytic converter was just installed about a month ago at meineke.

I'm gonna take your advice and order a new pigtail plug for the alternator since wiggling it makes the car die.. obviously the plug is screwed, but the low voltage output from the alt.. I will go get a new alt. tomorrow morning and install it. if it helps I will be very glad.. this cars been through a lot!

Yeah... You'll have that with the ebay header's. Wasn't the wrong one, they're all like that. No where near a perfect fit.
It seems like the only issue is that little bit of wiring. Don't get a new Alt. until after you change that wiring. No use in spending more money unless you are absolutely sure it's the Alt. Or if you would just prefer a new one. :-P

[97Supra]

well, this one is from a 95 geo prism, we pulled the engine and put it along with all attached accessories into this 95 celica ST (same engines) the differences were negligible but the alt looks to be original it's definitely got no wrench marks on the bolts so it's time to spend on a new one for peace of mind i guess

[cyberblader1130]

well, this one is from a 95 geo prism, we pulled the engine and put it along with all attached accessories into this 95 celica ST (same engines) the differences were negligible but the alt looks to be original it's definitely got no wrench marks on the bolts so it's time to spend on a new one for peace of mind i guess

I hear ya there, mine was original but i ended up having it rebuilt by a shop i trust. Didn't have the money for a new one quite yet.

[captb]

I had a similar problem but mine would die out sometimes. I eventually replaced the fuel filter and it made a world of difference. Not completely sure it fixed the problem but so far 1 week with no problems. If u havent done so yet u might want to consider fuel filter.

[SwissFerdi]

I think I might have to do mine as well gents, I notice that I have a somewhat rough idle sometimes.

[97Supra]

did the fuel filter when we pulled the motor..

Just got back inside just replaced the alternator with a new new new unit, still idles just as bad as before..

so i adjusted the idle stop screw to set it higher since it idles constantly at 650-700 at most .. and that did nothing at all. I'm starting to think there is an internal failure such as a burned valve or something of that nature because the engine was pulled from a vehicle (unbeknownst to me having this idle issue) I have since replaced absolutely every sensor and everything on the exterior of the engine and not a single thing has made any impact on the rough idle or idle speed what-so-ever.

intake manifold / throttle body / all sensors / exhaust with cat complete / intake / entire fuel rail, injectors, pressure regulator, EGR valve, all vacuum hoses, PS pump, alternator, belts, distributor, entire tune up including fuel filter cap rotor wires plugs, new grounds all over, double grounded battery cable, new terminals, set timing, fresh fluids, changed motor mounts... I forget what else

This has been a tremendous waste of money thus far and I'm just going to have to pull the plug on searching for now, it's going to be looked at by a mechanic my father uses so we'll see what they have to say. If they can not figure it out either, I'm just going to make sure it passes inspection and drive it into the ground. I have an MR2 turbo I waste all my money on, this cars eating up too much. I'll post back with results from the shop in a week or so.

[SwissFerdi]

^ Without seeing the bill, I can agree with you that it's too much...but your situation is VERY atypical of what I've read and heard (and know) about 6GCs. Hope you find out what it is soon.

This post has been edited by SwissFerdi: Mar 8, 2011 - 2:43 PM

[cyberblader1130]

Fuel Pump?

[Tigawoods]

going through the same problem. everything i do doesnt help
waste of money

[97Supra]

The fuel pressure was to spec according to the haynes manual, and that sucks.. a lot of people seem to be having horrible idle issues after a certain time and then nobody figures out what it is.

My brother texted me and said his boss told me to change the intake manifold gasket - says they are prone to leaking on these engines. I don't know if he knows the celica has like 5 different engines but.. If it turns out to be the intake manifold gasket I'm going to laugh... because I reused the old gasket in a pinch I was unable to go to the store, but I don't think that's it because removing the manifold and putting the other one on should have sealed it when i retorqued it. I suppose anything is possible but.. from my experience usually bad vacuum leaks don't cause a low or crappy idle they cause a high smooth idle.. but I have never seen a car idle this bad, and run perfectly off idle before.

[stephen_lee]

if youre really worried about the internal condition of the motor, do a compression test...

both my 7a autos idled at 600-700 in gear once warm. its rough but its how itts supposed to run apparently..

but i got a fix

add a 330 ohm resistor inline with the ecus coolant temp sensor. its the 2 wire CTS on the water neck kinda pointing towards the throttle body.

this will raise idle to about 1000 in neutral, and 800-900 in gear. if you think thats a bit much try the next smallest resistor.

This post has been edited by stephen_lee: Mar 9, 2011 - 7:46 PM

[97Supra]

Compression test results:

Cylinder 1: 205 Cylinder2: 190 Cylinder 3: 195 Cylinder 4: 195

It failed emissions which is the only reason I'm even trying to fix it so I can pass inspection. Drive legal my friends

[stephen_lee]

motor should be okay then. raise the idle and it should be smooth sailing (err, driving) afterwards

i did it to my daily and its helped A LOT. takes a bit longer for the ecu to decide its ok to use 4th though. but i can live with that over the shaking...

[97Supra]

I'm definitely going to try this for the comfort of the ride if my fathers guy cant figure it out, because every time i stop i feel like the cars going to crumble into a pile of bolts. haha

[windowlicker]

do a cylinder leak down test.

[stephen_lee]

how'd this turn out?

[97Supra]

got the car back, it passed inspection and the shop couldn't figure out what was wrong.. all the owner .. a tech of 30+ years could say was:

"Adjust the hard idle setting with the screw, and change the motor mounts."

I already DID change the hard idle and somehow no matter how high I put it, it wont idle higher than like 700 with it way out where 1,000 should be and the mounts aren't causing the needle to fluctuate. When I start the car, the car is searching for an idle speed that it's hardly able to steady.. it doesnt jump a lot, but it fluctuates 200 rpms at least up and down for a few seconds and sometimes at lights it dips too far, or raises without throttle input. It's like a vacuum leak but I retorqued the manifold gasket, and sprayed carb cleaner all over the engine.. the rpms didnt change and I was using a timing light so I'd have a dead accurate reading of the rpms.

I have a set of cleaned up injectors I'm going to install with new rubbers, and I'll change the intake manifold gasket with a brand new one. If the new gasket doesn't have any impact, I'm going to probably give up.. I already have the gasket so I might as well.

[clownpRon]

I tried to solve this mystery, but gave up after a few failed attempts. Now I just throw it in neutral when I'm at a stop.

[97Supra]

If I figure it out I'll be sure to post it up because this is a pretty annoying issue, having to daily drive a car that literally is shaking itself to pieces is not something I can settle for. I put it in neutral also, but it still shakes just not as bad.

[clownpRon]

I'm pretty sure though it's the throttle body on mine. It started after I installed my SRI, I believe. I feel now it has to much play. So when it shakes it then shakes my hood and makes a lot of noise. But this is all in theory. I cleaned the throttle body out with a rag and deep creep and it shakes less. Random hard spurts. I just need to go back in there with a brush and go to town.

[stephen_lee]

raise the idle with that resistor guys. the idle is a factory spec 650-700 rpm. i induced a vac leak before to raise the idle (pulled that vac line of the top of the TB, closest to the front of the engine) it raised the idle...then the ecu "learned" and dropped it back down to 650ish when i plugged the line back in it dropped to 400 or so... then eventually raised back up to 650-700.. that resistor seems a permanent fix. 1 month so far

[Bitter]

you can't just change the throttle stop screw, you also have to recalibrate the TPS when you adjust it! Also, yes change the front and passenger side motor mounts to start with.

[delusionz]

You haven't unwittingly used Polyurethane engine mount bushes have you?

[brenton1919]

If I figure it out I'll be sure to post it up because this is a pretty annoying issue, having to daily drive a car that literally is shaking itself to pieces is not something I can settle for. I put it in neutral also, but it still shakes just not as bad.

dude i really think its your flywheel it may have came lose or lost some blots out of it your egr would make your car shake like hell if its bad but u said u changed it tho check your fly or check your harmonic balancer you might have a lose rod to i think your flywheel came lose tho my lil brother does it all the time he breaks the blots and the car shakes like hell

[zfjohnson07]

my car shakes like hell as well, today for some odd reason it stopped for about a min, once it gets to 900rpms its rough, so i throw it in neutral and rev it to 2000 rpms and it is fine, but like clownprob said clean your throttle body, someone recommended that to me.

[stephen_lee]

if theres a bottom end problem (balance, rod) it would get worse as RPMs rise.

[97Supra]

i still haven't found the issue.. but that shiny new alternator they sold me at advance auto parts failed already its grinding inside.. going back today to exchange it... man i wanna junk this car but i just gave up my truck and sold my Mr2 so I'm stuck with this thing until I save up enough for something else.

[zfjohnson07]

well not to jack your thread. been searching for it but how do you change the idle i know its a screw on the throttle, any pics

[97Supra]

The hard idle set screw is what the throttle pulley rests on, (half moon that the cable is attached to) comes to a stop at one end of the screw. There is a small nut to loosen it up and it is a small metric alan key which turns it if i recall correctly. The throttle position sensor will be out of sync if you change the hard idle.

[csscza]

Im following along mine just got back on the road and is now vibrating at idle a little once in awhile

[brenton1919]

Im following along mine just got back on the road and is now vibrating at idle a little once in awhile

harmonic balancer

[Jaws4God]

having a similar issue.. haven't really done much yet cuz not sure where to start... my car starts fine.. idles around 1200 or so until it slowly drops to the 700 or so normal.. but then it will start dipping VERY low on RPM and almost die (like 200-300rpm).. but will keep running.. very rough idle... then after i drive for a few miles, its still running a little rough, but is back to idling around 600-700... any ideas??


5sfe - 5spd

This post has been edited by Jaws4God: Sep 28, 2011 - 2:22 PM

[stephen_lee]

on the rear of the throttle body theres a small plate thats mounted/shaped similar to the TPS.

loosen it and rotate it. it will adjust the minimum opening angle of the idle control valve

[Jaws4God]

on the rear of the throttle body theres a small plate thats mounted/shaped similar to the TPS.

loosen it and rotate it. it will adjust the minimum opening angle of the idle control valve

thanks! i found that and adjusted it so now it idle's around 1000... so hopefully if it tries jumping down low on RPMs, it will still have plenty of RPMs left..

however it is still running a little rough.. like i have a miss-fire.. so not sure if its still a vacuum leak.. or spark plug.. spark plug wire... etc... not sure what how to test next...

[stephen_lee]

on the rear of the throttle body theres a small plate thats mounted/shaped similar to the TPS.

loosen it and rotate it. it will adjust the minimum opening angle of the idle control valve

thanks! i found that and adjusted it so now it idle's around 1000... so hopefully if it tries jumping down low on RPMs, it will still have plenty of RPMs left..

however it is still running a little rough.. like i have a miss-fire.. so not sure if its still a vacuum leak.. or spark plug.. spark plug wire... etc... not sure what how to test next...

i would do a tune up if it feels like its misfiring

[bluecelica1]

The hard idle set screw is what the throttle pulley rests on, (half moon that the cable is attached to) comes to a stop at one end of the screw. There is a small nut to loosen it up and it is a small metric alan key which turns it if i recall correctly. The throttle position sensor will be out of sync if you change the hard idle.

You might want to switch those vaccuum lines on a/c vsv located on the wall.

[Special_Edy]

pull all four spark plugs(keep them in order) and closely compare the colors to see if one is rich or lean. Also try a cylinder balance test. With the engine running use a rag to pull the spark plug wires one at a time, the rpms should drop and the engine will run rough. If one cylinder has less of an effect on the idle speed when you pull the plug wire than that is your weak cylinder.
A compression check wouldnt be a bad idea either, they have a loaner one at autozone