94 surging/bucking problem

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hello
i have a problem with my 94 that is puzzling me.
6speed 140k miles no ses light service ride control (z07 option) light is on, but that is a bad servo that
i know about no other indicators on new battery alternator normal output all other temp indicators in normal ranges
the symptoms started a few months ago. in top gear at high way speeds, it will seem to miss when a demand is placed on the engine (going up a hill, passing, etc). in the ensuing months, it seems to have gotten worse, in that it now:
at idle (which used to be around 800rpm), it would start to hunt, going from 800-2000, with no throttle input. during around town driving, say in 4th at 45, the engine would speed up so the car would accelerate, with no throttle changes being done by me. the pedal doesn't move under my foot, so it's not a spring, i believe.
i replaced the iac valve and airfilter at this point. when the old one iac was removed, it had a lot of crud on it. i cleaned out the opening to the throttlebody, but didn't take it off for a complete cleaning. i also replaced the water temp sensor, as i noticed the harness connector was cracked.
the problem has now changed, in that the idle has dropped to an abnormal low of 400 and seems to almost stall. it still has the missing and bucking at constant speeds, and also misses pulling away from a stop.
i took it to my local mechanic, whom i've had for about 20 years. he noticed that every time it surges, the service ride control light changes intensity. he seems to feel that the computer is bad and is affecting the timing somehow, and said i should take it to the chevy dealer.
could this be a fuel delivery problem (fuel pump, filter, bad injectors)?
are there any other sensors that this could be, or does this sound familiar, and if so, are there tests for them so i don't have to start throwing expensive parts at the problem?
thanks, charlie cave creek, az
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you could try running some Lucus fuel injector cleaner through a tank of gas, then replace the gas filter.
my2
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"Key"
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Key had a good point, but I am also thinking possible OptiSpark issue. Could be either side of the equation really, fuel or spark. Frustrating!
charlie wrote:

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Ric Seyler
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actually, before i replaced the water temp sensor, that plug had fallen out, and the engine went from occasionally missing, to missing constantly and not having any power at all, basically stranding me. when i plugged this sensor cable back in, it went back to the odd and occasional miss. that's what led me to think it may be some bad sensor or even a wiring harness problem.
i guess i'll try the fuel cleaner and filter first. dumb question: where is the fuel filter? i have a shop manual for this car, but it must have been a pre-release version, as a lot of the sections seem to be missing, stating 'see 1993 year manual for this section', and most of the engine sections are missing. the manual came with the car, which was a very early 94 press car.
thanks, charlie cave creek, az
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on an 89 the fuel filter is along the inside of the frame rail just behind the right front tire. not real sure if its the same place on your 94.
g'luck
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"Key"
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On my 93 convertible, it's there under the cross brace.

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On my 1990, its the same as the 89 - strange place to have one. You have to remove the tire to get to it (unless you can elevate the car).
Empty3
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This is a multi-part message in MIME format. --------------050709030808050706080407 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit
charlie wrote:

Maybe take it and have it scanned?
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When was the last time the spark plugs were checked/changed?
charlie wrote:

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100k miles ago, at least.
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charlie wrote:

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nope. it still gets 24mpg in town, 30mpg on long distance trips. this is my daily driver as well as my long distance traveler. i put on 300+ miles/week commuting, and multi-thousand mile trips. it's been rock solid for over 10 years. why fix something that hasn't been a problem?
i don't think bad plugs/wires will cause surging, uncalled for speedups, idle seeking, and higher or lower than normal idling. it might account for the missing, but unless 2 problems happened at the same time, there's something else going on. i asked over at the corvette action center, and someone suggested an egr, which also has never been replaced since i got the car. that, i believe, can cause this problem, and seems to have the same symptoms that others have seen elsewhere.
regards, charlie cave creek, az
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All the guys that go 50,000+ on the original spark plugs are all losers. This is a losing thread.
wrote:

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charlie wrote:
>>> i have a problem with my 94 that is puzzling me. > > 100k miles ago, at least.
I've never replaced the plugs in my '93. I'm still running the ones from the factory. It still runs great. I've only got 62K miles on it though.
I had a similar symptom on my '85. The pro's diagnosed bad fuel filter, then bad fuel pump. When the after market fuel pump that they put in it failed, I took it to the Chevy dealer. The Chevy dealer told me it was the injectors, and charged me a fortune. It finally turned out to be the MAF.
Hope this helps.
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thanks. hope not. wouldn't a maf failure throw a code?
i actually had almost exactly this same symptoms on my 89. many hundreds of dollars later after the pros replaced the egr, injectors, maf, maf relays, it turned out to be the iac. that's why i tried that first, and unfortunately, it wasn't the same problem.
regards, charlie cave creek, az
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charlie wrote:

I'd check them cause it's one of the things that won't throw a code, and it fits both symptoms in my 95 manual.
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I have an '84 crossfire and have a very similair problem.. When at low spped with no extreme power requirements the engine 'surges', I have replaced virtually everything (including the power brake vacuum booster) thinking it must be a vacuum issue. I am down to the point that it is probably the injectors but on the crossfire they are about $600.00 each. I'm saving my money for the two injector replacements now.
I hope this works or I think it will force me to result to carburation.

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my 84 done the same thing. don't be to quick to replace injectors. Is your fuel tank clean of debris? have you checked for proper fuel pressure? did you check/replace fuel pump, and fuel filter? have you run injector cleaner ? (recommend Lucus Fuel injector cleaner)
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I have not replace the fuel pump but have checked it at most rpms and it is steady, I have run several injector cleaners, replaced the fuel filter and tps, new cam, rollers, solids, but had issue prior to new cam and solids, I have even replaced the brake vacuum booster thinkingit may be a vacuum issue.
I am down to the injectors or I dant know what accept maybe the ECM?
Art

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well, I am out of suggestions. maybe someone else here will be of help? when you find out the source of the problem. please return and post it. I am courious to know.
g'luck
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"Key"
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