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Stuttering At Idle

by Zair, May 4, 2007



Hi,

I have a '97 Geo Prizm with 104,000 miles on it. It's been pretty well taken care of, with regular maintenance and I never drive it very hard. I've had it since it had 45,000 miles and I've had nary a problem. It's a 3-speed automatic, the 1.5 liter non-lsi version. It's never broken down or had any major issues of any sort. One thing that it has started doing though within the last 20,000 miles or so is stuttering when at idle.

This only happens when the engine has warmed up. I'll pull up to a stop light and the engine will ocassionally stutter. It's almost like it wants to die, but it never has. Sometimes it will stutter slightly when I first start to accelerate, but it's never for more than a very brief moment. The stuttering seems to come and go. It will do it fairly often for a couple weeks, and then not at all for a while.

I've replaced the spark plugs, the cap, the rotor, cleaned out the throttle assembly and IAC valve(which was actually amazingly clean for a car that had 95,000 miles on it!), I even replaced the MAP sensor and to no avail. One thing I haven't checked is the spark plug wires, but I don't know if they would even go bad. I know my transmission fluid is in need of changing (it's quite brown), but I don't think that can be the problem, since my transmission fluid was relatively new when the problem first started. Otherwise, I never need to add oil or coolant...

My gas mileage has dropped since I got it, though. I used to get 26-28 city, 32-35 highway. Now I get 23-26 city and 29-32 highway. I had the fuel injectors replaced and got the whole fuel system cleaned and the filter replaced, but that didn't seem to help much.

Finally, the stuttering seems to increase when I'm in drive, gets even worse in reverse (the one time it ALMOST died was in reverse), and having the a/c on makes it worse as well. My fiance's dad hooked my car up to a tachometer, and it was idling around 700, which I think is okay. Though I don't remember, I'm pretty sure that the RPM drops when it stutters.

That's about all I can think of for now. Anyone have any ideas? This problem has been a real stumper. Let me know if I can provide any more information.

Thanks,

Tobyn

Spark plug wires do go bad - I would have them replaced when you did the cap and rotor. Chances are - it is an emissions related issue (loose or leaky vacuum hose) or a sticking EGR valve. Also be a good idea to check your ignition timing - make sure that is not off. How about timing belt - recently replaced? A bad a or faulty ECT sensor and lazy O2 sensor can cause poor drivability and idle quality.

Spark plug wires do go bad - I would have them replaced when you did the cap and rotor. Chances are - it is an emissions related issue (loose or leaky vacuum hose) or a sticking EGR valve. Also be a good idea to check your ignition timing - make sure that is not off. How about timing belt - recently replaced? A bad a or faulty ECT sensor and lazy O2 sensor can cause poor drivability and idle quality.

Hmm, I'll replace those wires then; better late than never! I found in my service manual how to check for proper resistance in the wires, so maybe I'll do that first, assuming my cheap multimeter will do the job.

How would I go about checking the vacuum system? I've inspected all the hoses that I can see and nothing seems cracked or worn. I don't think I've checked the EGR valve. Is that something I can clean out, or will I need to replace it? (Also will I need a new gasket for it if I do take it off? I'd like to know BEFORE I remove it default_laugh )

Finally, I hadn't thought about the ECT or O2 sensors. I don't think I have the tools to check either of those out (though maybe my repair manual might help; I do have that multimeter), but I can probably get them checked out somewhere.

Thank you very much for your quick (and very knowledgable) reply. As I've parused the forums over the past few days, you always seem to have excellent advice. Much appreciated!

-Tobyn

Good call on measuring the resistance of the wires - as they may still be OK. Just check for the obvious oil soaking, burns, and cracks in the insulation and ends.

Vacuum diagnosis is always tough - fortunantely, you can catch a majority of the problems with a quick visual inspection of the hoses. Replace any that have hardened or cracked.

EGR valve usually gets clogged up with carbon - causes the valve to stick open causing a funky mix of fuel, air, and exhaust gases - idle basically goes everywhere. Much more significant when you travel down an exit ramp and come to a sudden stop - sometimes the car will almost completely stall or idle is way off. That's a sure sign of a sticking EGV valve. Does have a gasket - a metal composite one. Should be pretty cheap to pick up - new EGR valve will probably set you back at least $150 - worth a shot to try and clean it first. There is also a vacuum modulator that has a little air filter in it - might be worthwhile to check that too - part of the EGR system as well as a truck load of vacuum hoses. Glad to hear you have a service manual.

You can check the ECT sensor with a multimeter - I would not try checking the O2 sensor unless your multimeter has a very high impedance. Also do not try and measure the resistance of the O2 sensor - that will quickly damage the sensor.

Without my service manual, I'd pretty much be totally lost! default_wink I'll give my EGR valve a good examination and cleaning next week when I should have some spare time! I'll check back in and let you know how it goes when I get that done.

I can say that I've never had any noticable hesitation/stuttering when coming to a stop coming off the freeway, or anywhere else. It actually happens mostly AFTER I've stopped and I'm sitting at a light while still in drive. I find it happens much less often when I switch it to neutral. Nonetheless, as I haven't yet checked the EGR valve, that's a good next step along with the spark plug wires.

Hmm - could also be a leak in the induction system. Could be as simple as a cracked or loose piping to the throttle body or a loose intake manifold, I've seen weirder things happen. Good Luck, let us know what you find out.

dont forget to look at the plugs as well, one or 2 bad gaps can do some weird things.

I've decided to examine my spark plugs and make sure they're gapped correctly when I test the wires. However, I can't find out what to gap them to! My Chilton's manual is bloody useless on the subject. After searching the book to find the tune-up specifications (why oh why could they not just specify the gap settings in the same place where they tell me 30 times to make sure the gap is correct?), it tells me to gap them to 0.31 inches. Almost a third of an inch?? That seems... terribly terribly wrong. Perhaps they meant 0.031 inches?

I've double checked that page three or four times, and it definitely says .31 inches, and it repeats it for every single Corolla model from 1988-1997. So either I'm nuts or .31 inches is an acceptable gap. I suppose either one is possible.

Suffice to say, I don't trust the manual one bit on this matter. Does anyone have a manual with correct values in there? If so, what is it? (1997 4A-FE model)

Thanks again,

-Tobyn

I'm pretty sure it should be 0.031" - as most sites indicate aftermarket plugs should be gapped 0.031" - 0.032" (ie. sites like www.sparkplugs.com).

I'm pretty sure it should be 0.031" - as most sites indicate aftermarket plugs should be gapped 0.031" - 0.032" (ie. sites like www.sparkplugs.com).

sparkplugs.com. Genius!

Well, I hate to keep asking questions without actually having gotten anything done yet (what a busy week its been, and the weekend looks even busier!), but I have another question anyway!

In my investigation into spark plugs, I've found that AC Delco plugs for my car are gapped to .042 (that's what comes up for the recommendation for a Geo Prizm), whereas the suggestion from Toyota for the Corolla is .032. As far as I've heard my engine is 100% Toyota, so I'm not sure why the GM folks would have a different gap recommendation.

My question is this: How much of a difference would that .01" make in the performance of my car? Whom should I trust, Toyota or GM?

My feeling is to trust Toyota and gap my spark plugs to .032, but I don't know for sure.

Thanks again!

-Tobyn

My question is this: How much of a difference would that .01" make in the performance of my car? Whom should I trust, Toyota or GM?

Haynes manual for 93-97 - .031 gap

I'd suggest you clean the throttle body, but i saw in another thread you did that already.

Spark gap can make a big difference. Just get out your ratchet set and gapper..it only will take 30 mins.

Report back and let us know.

Guest FLYCARZ

I had the same problem with my 94 corolla, went to a junk yard and bought a used ignition coil for 5 dollars and this solved my problem , buy a cheap multimeter 15$ open the distributor cap , remove the rotor and rotor cover then check the positive and neg resitance of the coil it should be about 1.8 (1.75) ohms . put back evevrything and start the car let it warm up to normal temp switch off eng and open distri again measure the resistance again if it fluctuates like crazy its the coil thats a mess. In my case this is how it was behaving. I had swapped the water temp sensor,iac,map, ac idle up valve, air intake sensor, tps, flushed the transmission cleaned the throttle body and almost gave up, only to find a crazy warmed up ign coil.Hope this helps and saves you the trouble and money



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