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4.9 92 Fleetwood - weird one time high rpm

367 Views 3 Replies 2 Participants Last post by  sefiro
Did some work and had a weird one time high rpm for about 5 minutes last night on first drive. Will get back into it tonight to see if I muffed something but figure I'd post here to see if it had happened to anyone else.

Old history way below but here's what I have done lately.

Had replaced all the injectors some 18 months ago after the second and third failure in 6 months. Things ran great for 12 months and then developed a rough idle that has getting slowly worse. I must have sprayed enough cleaner around the vacuum to clean an 18 wheeler. Nothing.

Lately, it started throwing a intermittent TPS code so figured it's time to solve it. Did the world the TPS pigtail thing and no code set, ok, replace TPS as item one. Went looking for vacuum leak again. Did the tuneup thing setting isc, timing etc. and realized I could hear the misfire more clearly than on a normal gm misfire. Focus EGR. Could not get it to activate (yes, it is a positive backpressure assisted design). Concluded the diaphragm is closed and the the valve is open a bit and the seal around the pintle is gone.

Both are warranted at the local 5&10 so I replaced them last night. Idle great. Did the TPS relearn thingy and took it for a ride (1 AM). Ran great for the first few minutes. I then noticed it was driving itself and had to mash the brake to hold a stop. A few more stop and goes and pulled over to look. Put in park and engine started racing, killed it. Restarted and continued racing, killed it. Popped hood (2 miles out from garage) and could not see anything unusual. (TPS and EGR only required removing reinstalling 4 vacuum hoses and they were in place). Restarted and threw it into gear before rpms got too high. The brake mashing continued for the next mile back and then everything returned to normal. No codes.

Since no codes, then PCM commanded this and received appropriate response (ie, no ISC/RPM/TPS out of range codes.

- continuing TPS/ISC relearn?
- need to reset computer by pulling battery etc
- faulty TPS (yes, 5&10 can sell cheap junk)

Old History
Kids' HS and College car for about 10 years. I got it back 3 years ago and finally got caught up on things and use it for the weekend referee car. (Especially useful when on the other side of town).

Posted about the mpg search here:

Items replaced in the past include TPS, EGR, Injectors, ISC, plugs, wires, distributor, Coil and regular oil changes.
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Did you properly adjust the ISC motor plunger?
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