Cadillac Repair: high idle and rough running engine, throttle position sensor, o2 sensors

Question
Bill: I have a sedan deville 1995 with 55000 mi.   About 300 mi back the engine began to miss while under acceleration. Later the skip (stumble ) became more obvious, not just under a load but even after warm up at idle in the driveway. In an attempt to find the problem, I have replaced the plugs, the plug wires, the dist. cap, the rotor, the coil, front and rear O2  sensors and the pcv valve. Nothing changed. I then used some gummout on the butterflies and the carb throats to clean out some carbon residue. the stumble(miss) is still there but now the idle has gone bonkers. After start-up on a cold engine, the rpm will wind to about 2000 and it seems to take forever to come down to normal (about 800 rpm) and after warm up, it still skips. If I take it on the highway, once its up to speed, take your foot off the accelerator and it will take a half mile to slow down. My brakes are taking a beating and it still skips.
Any ideas you might have would be appreciated. I do my own work but I may have reached the limit of my expertise on this one. Thanks. Lee


Answer
Hi Lee, After giving this some thought I feel that there are several issues going on here. By cleaning the carbon from the throttlebody plates and bore that can get rid of a stumble or hesitation when you first step on the gas. Useing the wrong cleaner or too much of it near the TPS, throttle position sensor, might have contaminated it and is the reason for the high idle all of a sudden...Since 1990 Cadillac has an idle learn procedure that must be followed in order to prevent a high idle and along with the relearn procedure is a check and adjustment procedure of the timing, min. air or base idle speed, tps setting and finally maxamum isc, idle speed control motor, extension. Any of those adjustments that are off can cause a high/30 mph idle. If the battery was disconnected and then reconnected then this relearn procedure needs to be done. You will need a shop manual and test equipment because this is too complicated a serries of tests and adjustments to explain in this forum...The other thing that could be happening is that 1 or more fuel injectors are starting to short out or have reduced fuel flow. If the engine starts to idle rougher as the engine reaches operating temperature then fuel injectors need to be tested. They cost around $85 to $130 so putting in all 8 would get to be expensive if they weren't all needed. Sounds like this might be time to have a tech repair the problems because without hooking up a scan tool and varrious other pieces of test equipment it would be tough to know what to replace next because you have already done the easy stuff that could fix a problem such as this...Also if the check engine light is comming on now then it is definitely time to find out the current code(s) and that might lead to the fix. Sorry I can't be more help but your caddy is a complicated automobile and can stump the best of us for awhile. Bill