I purchased a 97 C2S in November with aprox. 39k. Car ran great when I purchased it and the PPI did not reveal any of the problems that I will describe below. I parked the car for the winter and took it out of storage this spring. Sometime this spring I began noticing that when the car was first started and cold that the car would hesitate and run like crap when I first began to drive down the street. After the car would warm up, you could feel a rough idle in the seat of your pants. The rough idle felt like it was isolated on the right side cylinders. I cleaned the ISV, per the DIY, but it did not seem to help. Additionally, the care did not seem to rev through the 2-3k range as well or freely as when I bought it.

The rough running at idle and rough idle when warmed up did not trigger a CEL and the bulb is still functional. I took it to my local mechanic who seemed perplexed by the issue, but also indicated that he did not have the complex electronic equipment to analyze. I then took the car to the dealer who ran an OBD II scan and found nothing and seemed to think that the spark plugs were bad. The plugs were changed after it was found that the previous owner only replaced the easy plugs at 30k. The car seemed to run marginally better with the new plugs, but the problem with the poor performance when cold and the rough idle when warm still persists. I did not return to the dealer fearing a huge bill associated with the mechanic poking around to find something.

I recently changed the DME relay, with no improvement. in performance. The only possible problems that I can see is: (1) slow O2 sensors that have not yet triggered a CEL, if that is possible (2) a vacuum leak (3) bad plug wires or cap/rotor that was overlooked by my mechanic and dealer. However, it appears that the caps/rotors were changed.

I appreciate any possible theories or input regarding this problem.

 

Did you change the gas that had been sitting in it all winter?

 

I kept the same gas, but added gas stabilizer and followed the recommended winter storage tips. I also allowed the ECU to relearn after re-installing the battery.

 

Did you check the distributor belt... seems that it's caused similar problems for others

 

BTW, what part of Toledo are you in? I was just in Perrysburg over the 4th... enjoyed the local fireworks and painted my mother-in-laws garage in return for about 40lbs of her world famous lasagna... I made out like a bandit on that deal, though my neck is still sore from the 5 straight hours of painting the garage ceiling.

 

bad gas or wiring harness

 

Yea, I checked the belt operation. I forgot to mention that in my prior message. I actually did the basic test where i disconnected the plug harness for the primary distributor cap and was able to start the car using the secondary system. My mechanic also looked into it and found no issues. Thanks for bringing that up and reminding me.

 

I actually live in the Springfield/Sylvania, which is not too far from Perrysburg. If you are ever in the area, PM and we can swap car stories, etc. In response to some of the other theories, I would have thought if there was bad gas that it would not be an issue by now. I have ran some Techron through and some Chevron fuel injector cleaner as well. I have probably filled up about 8 times since winter as well.

 

Could be some crap in one/some of the injectors that the injector cleaner failed to clear.

Putting the car on a crt ignition analyzer should tell you if bad wires/rotor/coil are culprits.

Chip

 

Check P-car.com for the DIY regarding the ISV. This could be your problem. I had some of the same symptoms so I did the ISV DIY, ran a bottle of Techron through, did some really spirited driving, and voila!...no more issues.

 

replace your plugs. sounds like they are fouled

 

Did you by chance have a compression or leak down test at the time of PPI? Since you have covered most of the easy quick fix items, try a large bottle of Techron, followed by an Italian tune-up.. Get her good and hot and go for a hard drive..