weeding out the rat

okay everyone... this is a '91 corsica 3.1 v6 154,000 mi., 2nd owner, all service records, bought at 100k.
It started to be, what seemed like a miss, idle and drive. So I began to track this little varmit of a miss. I changed the plugs and wires, it wasn't there. I changed the ignition module and it ran great. I felt good, like I was king. Then one day when I was cruisin' around feeling good, it happened again. The little miss of mayem was back. Furry gripped me, for my foe would not stand and face me like a man. It chose to hide and lurk about, then strike like a terrorist. So I went to war. I hit it with a fuel filter, an air filter and a dose of injector cleaner. Next came a new thermostat and heater core, just in case. After that it was a pcv valve, new vaccum lines and an alternator. Then I went digital on it's a-- with a TPS sensor and a MAP sensor. And that's when he went and got his friends... service engine code #33, gas guzzler and the rest of the miss family. What have I done? How do I get my car back? Is it ecm or maf, or o2 sensor or timing chain?
All help will be appreciated, I really don't want to put her down. Rob :banghead:

Code 33 on the 91 is MAP sensor trouble, although a miss can trigger it too, according to GM manual. Check the connections, then, check these for your miss problem. A constant miss could be a defective plug, wire, injector, etc., so you have to rule these out. Would NOT be a timing chain. Possible your EGR valve has bit the dust although you should get a code there... If the miss is at idle you should check your rubber boot going into throttle body, if it is cracked it will cause running issues on your engine (assuming it is multi port fuel injection like ours), and the main thing to remove and clean is the IAC (idle air control) which should be on the front of your engine on the throttle body. Removes with two screws, has a connector runing to it as well. These carbon up and will cause a poor idle. Be careful not to push the pintle in (spring assy) just remove it, clean it with good carb/injector spray and maybe a tooth brush, paper towels etc. to remove all carbon deposits. Also clean the area it sits in. A plate with 3-4 screws is beside it and will let you clean further. (be SURE to unhook battery before removing the IAC, and when you restart car let it idle to re learn idle. Our 91 has been thru about all of the above things, can be a pain to fix, but usually as long as the IAC is clean, plugs are good, wires, and TB cleaned and a good soild intake hose, they won't misfire unless a sensor has failed. AN O2 sensor will cause poor running, a cheap fix, but usually sets a code 13. Replace anywy if over 60K miles. You do not have a MAF sensor on your car. Your ECM should not be a problem unless you have the car running well and it is still setting codes that lead nowhere. Ours failed and kept setting codes for EGR, MAP, O2, the works even though all were replaced or tested OK. Sometimes a sensor won't set a code and other problems can cause a code to set, ie, a miss can cause code 33 even if the MAP is OK. I would not rush out to buy more new parts, too expensive to keep doing that, but check the hose, MAP connections, IAC and it's area, d/c plugs and wires (I have bought both with defects) and maybe go ahead with the O2 if it is old (a cheap item) and see if any of this helps out.

Sorry I did not mention this before, not sure why I did not... If you have a BAD miss, you might have another problem. When you replaced the ignition module, did you replace or check the three coil packs sitting on top of it??? Each one controls two cylinders, and usually one will fail and cause a dead cylinder (or two). They are about 20 bucks each, might check to see if you are getting fire to all cylinders.

Thanks for the advice. I will post when I give your suggestion a go. What you said makes good sense. I often take for granted that everything new is good. Rob

Hoorah!!! The rat is dead! I took your advice and started with the IAC. Then I proceeded to check the coils and wires. When I got to the back three wires, I noticed the end of vacuum line (a jagged end). Apparently when I replaced the pcv valve, I broke one of the small lines that runs under the fuel injection. I don't think this was my problem in the beggining, just one I created to prevent me from reaching the end. I really appreciate your insight jsgold and everyone else who posts on this site. It has saved me lots of money, my car, and possibly my relationship. Good luck to all in their automotive adventures. Until next time... Rob