My car seems to have the same miss and hesitation problem as many others have posted. Rough idle, and bad hesitation/stumbling in OD only, below about 1.5K RPMs. Idle has been rough for a while, but the hesitation thing is somewhat new, and was only when it was hot out, but now it's most of the time. When it first happened was real bad and I reconnected the accel 300+ ignition I've had on the car for years(was unhooked cause I broke the connector to the coil) and it got way better for a while, now it's geting bad with it on. Also I let the car sit for about a week, first time in a while, and this morning it was idling for a few mins and died, thats never happened before.

I did a search and read through alot of the posts but didn't find the answers I was looking for, just alot of replace/clean this or that. I came up with Opti, wires, coil, ICM, MAF, MAP, EGR, O2s, Injectors, Fuel pump, filter, or ECM wiring as possible causes. My car has about 170k miles on it and I'm sure none of this stuff is in great condition, but I absolutely cannot afford to just start replacing parts. So where do I start, and more importantly how can I test all these parts to be sure where the problem lies? I know a good scan tool and a scope can do the job, but I have neither. I do have a volt-ohm-meter, vac pump w/ guage, fuel press guage, and a basic understanding of how to use them, I just don't know what specs are good or bad for each sensor or which pins to test and when.

 

did you try pulling any codes from the computer? do you have access to a scantool? if not try autozone or some such thing.

also, you didnt specify what year car, mods, etc, so its very difficult to provide detailed information on the diagnosis of your car. a sig line that has this info would help other members give you speedy responses to your query.

 

One easy quick test is to look under the hood with the car idling in the dark. Look for the spark plug wires arcing to the block. Common failure.

 

Car is 94 Z28 A4 about 170k miles
Shorty headers, cat, flowmaster, SLP CAI, 52mm TB, Accel ign+coil+wires
Thought that was in my sig, dunno where it went. Opti was replaced at 100k, mods were done at about 110K, I wanna say '01-'02ish. While all that was apart I also replaced almost every thing in question now, except the MAF, fuel pump, and injectors. Now that I think of that I may have lifetime warranties on a bunch of that stuff. Did plugs, fluids and filters(all of them) and cleaned the MAF, MAP, and TB/IAC at the beginning of last summer and it ran great for a few months.

No codes or SES light, atleast as far as the autozone scanner can tell. No sparks or visable burns on wires, they are the accel extreme 9000 w/ firesleaves on parts that are close to the headers so it's hard to tell without yanking them. Unplugged the MAF and O2s(diff times) and test drove but it still missed.