: 97 STS with intermittent hesitation

11-11-04, 08:44 PM
I have a ’97 STS with 131,000 miles. At 97,000 Cadillac installed a new short block due to excessive oil use. New plugs were installed at that time. All was well until about 115,000 when the car started to have rough idle and some hesitation on acceleration. I first though that it might be some bad fuel, since the problem was intermittent. I added some fuel system cleaners and injector clearers and always premium gas, but the problem persisted and is still there. The only code that comes up is for a general misfire. I’ve checked the EGR value, it is clean and moves freely, the FPR is not leaking, and the car has had the “fuel rail recall” installed. Several items of note: The problem is not always there. Sometimes the car runs like new, but not often and only for a few minutes. It does not seem to be affected by engine temp. The problem is there hot or cold. At cruise, there is no noticeable miss although acceleration may lag. Fuel econ. is still 18 city and 27 highway. The problem seems to get worse when the AC kicks in. Coolant levels seem stable; I’ve added about two quarts since the engine swap. Any suggestions would be greatly appreciated.

11-11-04, 09:26 PM
Hmm, strange I should read this problem today. I had the exact same thing happen on the way to work this afternoon. Same year ('97) except Deville. I would discribe it as a rapid stutter. Is that what you are expiriencing? Acceleration is still there but very slow. I thought maybe a coil breaking down but could not duplicate it by brake torqueing it in park. I'm not even getting any codes. Like you temp is normal. Also like you, fuel rail was recently done. I'm wondering if maybe moving those plug wires caused them some internal damage. In my case it sure seems like more than just one cylinder (more like all of them). That would make me think maybe ignition module. The thing that scares me is it seems to only happen when in gear. Please don't let it be the trans. :crying2:

11-12-04, 09:20 AM
Mine actually started before the fuel rail exchange and it does idles rough while in park. Also, it seem that the misfire is across many cylinders. If it runs rough for a while I'll get the SES light. I'll check the codes and the only thing that shows up is the general misfire code. If I really step on it, it will studder for a little bit then smooth out and then take off. No exhaust smoke. When I drop down to normal RPM and step on it again, same problem. However, once in a while, I put my foot down and she's off like a rocket. Someone suggested a head gasket, but I would think the problem would be more consisitant and I would be loosing more than two quarts of coolant in 30K. Thanks for your input.

11-12-04, 09:45 AM
As a quick spark check; pull off your spark plug wires. Look in the spark plug tubes for signs of moisture. The rears are a little crowded, but use a flashlight to check carefully. If moisture is found wipe out with a paper towel and a slim screwdriver. Look in the boot itself and make sure it is dry.

If spark plugs have been in moisture for a long period of time the spark plug insulators may be carbon tracked. Is so I would replace them, carbon tracking is hard to remove.

The metal contacts in both ends of the spark plug wires should be bright clean metal, clean as required.

Pull each spark plug wire off at the coil. Look for corroded terminals. If found, wire brush clean as required. If several are bad I would remove the coil pack to make it easier.