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.