Well looking around apparently I'm not alone with idle problems but here are my cars problems...

1 Nearly constant rough idle...tach needle generally stays still at 600-700rpm but feels really rough and chugs

2 Occasionally idle will start to flutter around and either die (or come close) or surge up to 1300rpm or so...seems to be most often after exiting from a freeway drive so maybe temp related

3 On one occasion car would hesitate at light throttle on freeway when under 2000 rpms...got off freeway and the tach was all over the place...missed the friggin delahoya fight over this incident

4 Poor Gas mileage...like 11.5mpg in the city

So far I have replaced optispark (as well as water pump and harmonic balancer at great expense) plugs and wires, IAC, fuel and air filters. Two different shops have had a go at diagnosing the problem including one that used to be a corvette only shop to no apparent avail. The car runs cooler after these repairs (water pump) but it idles the same. Opti went in last week and since then symptom 2 and 3 haven't occured but the idle is still poor as ever and seems even worse as the days go on. The shops say there are no codes and I guess the car was running rich before the opti replacement not sure about now also said engine didn't appear to have any internal problems. Car has plenty of power its just the damn idle. What's left to try..? Oxygen sensors? Ignition coil? Thats what a friend suggested I try next. My symptoms sound familiar to anybody? Any help or advice would be appreciated...thanks. The opti-water pump-harmonic balancer-plug wires repair was to the tune of $2500 and the wallet is getting lighter by the day.

Dan
1994 Polo Green Coupe Auto G92 134000 miles

 

Well, it sounds as if you've replaced a lot of possible culprits. I'm having intermittent idle problems, as well, although it doens't sound like you have the starting problems I have. It could be the MAF... try unplugging it to see if the idle improves. I emphasize "could" because it's no guarantee. Mine started right up with the MAF unplugged and idled pretty good, but replacing the MAF and the relays has not solved the problem (to the tune of $250, just in parts).

Others have suggested injectors... could be bad seal, bad resistance, or bad flow.

You said you already replaced the IAC, was that the motor? Or all related parts? It seems, from what others have said, that the idle pintle and such in the throttle body can get dirty/plugged and screw up the idle as well. I'm wondering if that's what is messing mine up.

In a way, it's good htat your problem is consistent... mine is intermittent, making it extra fun to diagnose especially, like you, I have no codes set either.

I took the "replace likely problem parts" route to no avail, so now I'm considering investing a bit more time in diagnosis, by collecting data on a laptop from the ECM to see if that gives me some definitive diagnosis of what's really going on. I don't know if it will pay off in the end, but right now I'm thinkin' it beats guessing which part might be bad (that gets expensive, as you noted).

Good luck!

 

I have the identical idle problems on my 87 coupe (L98). I have replaced Plugs, Wires, Cap & Rotor, removed & cleaned the throttle body, air idle motor. Re-set the TPS, replaced the intake manifold gaskets. I have no codes!!!!!
My gas milage is 17-18 in the city, which is good, I think?

What is next? Vacuum lines, Coil? O2 sensor?
Jim

 

Well to answer the question the IAC is that switch in the throttle body area that you were talking about. I'm taking the car back to the shop that did the optispark/waterpump/wires/balancer job tommorow morning and insist that they diagnose the car correctly this time. The guy said he was "sure" that the optispark was my problem with the bad idle and if it wasn't "it was his problem" so I think I will go find out what that means exactly. If they want another few thousand for anything at all I think I'll be going back to my regular Goodyear place. Out of curiousity, does anyone know of a competent shop in orange county,CA that could possibly be better at diagnosing my problem then I've had any luck with yet? jezuz I'd gladly spend $200 to properly diagnose my cars problem then pay for whatever was wrong then pay $65 and then $3000 in unhelpful repairs. I mean sure ther optispark and stuff could have standed to be replaced but hell you could reach into my engine bay blindfolded and find a part that was old and could stand to be replaced how bout somebody telling me which of the old parts that could stand to be replaced will fix my idle? Sorry just bitchin now...but anyway if anyone has anything to add that might be helpful please do thanks

Dan

 

I definitely understand your frustration with the diagnosis. I've been trying to do some of my own... check out my post on "Won't start or idle" if you want to get an idea of what I'm learning along the way.

If you're game, consider taking matters into your own hands and getting a cable and a laptop and some scanning software (you could get all this for a few hundred bucks, including a used laptop) and at least getting the facts about what the computer is seeing and doing.

I hope to get mine figured out this way... when I do, I'll post the solution.

Good luck!

 

But isn't that what I've been paying people to do already...they are the supposed experts not me. I'm handy with a computer but it would take quite a bit of time for me to learn enough about how to make good use of the information I got from it, certainly there must be a shop out there that would do this better then me don't you think?

Another person who gave me advice mentioned my problem could be internal engine like rings or stuck valve however this person probably hasn't ever touched a car that doesn't have a carbeurator(sp) Wouldn't I have low oil pressure and oil loss problems as well as problems at other then idle do you think?

 

Yeah, I can't disagree with you there... they are supposed to be the experts. However, in my experience (others feel free to chime in here with their experience... maybe even a mechanic, or two) they typical mechanic is trained in how these systems work and how to read codes and follow the repair manual in the step-by-step diagnosis of problems. But, when you run into something intermittent and without codes, then I think it becomes a whole different ballgame. Maybe I'm wrong, but I think few shop mechanics have spent a lot of time really analyzing data in situations like this to figure out exactly what is happening, and it may become their "best guess" as far as which parts to replace.

My experience is limited here. It would be great if a professional mechanic were to help set our expectations... should we expect professional shop mechanics to analyze all the data like you can on a laptop? Or, is that just expecting too much and would take too much time, so it's easier/faster/cheaper to just make an educated guess about which parts to replace?

 

Well I was unable to take the car in to be worked on again this weekend but I did take it out on the freeway for some testing. It appears that sustained high speed highway driving helps the idle some. There wasn't any of the part throttle hesitation or wildly erratic idle that the car had been doing before the opti was replaced. The idle smoothed out some after being off the freeway but even there the idle wasn't as smooth as it should be. Sadly I don't get much opportunity to drive the freeways all that much but I believe these findings suggest clogged O2 sensors or injectors more then anything major. I guess next step will be to replace O2 sensors and have injectors cleaned/inspected. On a sour note it appears my power steering pump might be nearing the end of its life as at the end of the highway ride steering was getting mighty heavy and a little noisy...I guess the longer then usual drive and presumebly higher level of heat from it was making that apparent. Theres plenty of ps fluid in there anyway. I don't think the 2 problems are related probably.