mx5mike Posted February 6, 2011 Report Share Posted February 6, 2011 What are the symptoms of a failing TPS? 1991 Old's Cutlass Supreme SL with 3.1 and I think 4t60? Hesitation/stumble at constant throttle at low speeds 20-38mph and a stumble rough idle. also the trans has harsh downshifts and seems to take a bit more throttle than normal to get a kickdown to pass. theres the symptons does this sound like a TPS? I have checked and tripple checks all vacum hoses, sea foamed, cleaned and relearned the IACV, plugs, wires, Fuel Filter, engine side lower mount and both dog bone's and a trans drain, filter and fill. this is driving me nuts.... TIA Quote Link to comment Share on other sites More sharing options...
Galaxie500XL Posted February 6, 2011 Report Share Posted February 6, 2011 A failing TPS isn't very likely to give you rough idle...I'd suspect a bad coil pack...been through this several times with DIS equipped GM cars. Get a plug tester, and see if you don't find your car is running on 4 cylinders rather than 6...keep in mind, each coil fires TWO cylinders, so when a coil goes bad, two cylinders are missing. Quote Link to comment Share on other sites More sharing options...
mra32 Posted February 6, 2011 Report Share Posted February 6, 2011 you can check it by backprobing the connector to the TPS with a multimeter. This is how I ruled out mine being bad. You can do this with the engine off, but the key on. It should be somewhere around .5 Volts at closed position and then you should watch the multimeter as you very slowly sweep the throttle to full open. I think 4V or 4.25 or 4.5V is where the computer sees full throttle, so the full open position should be there or above. The slow sweep is to watch for any faulty positions on the sensor, the sensor voltage might jump up to around 5 volts or down to close to zero in a small spot like this. But with those symptoms I might try to bark up another tree first, though the TPS was like $15 last time I checked. Quote Link to comment Share on other sites More sharing options...
mx5mike Posted February 6, 2011 Author Report Share Posted February 6, 2011 A failing TPS isn't very likely to give you rough idle...I'd suspect a bad coil pack...been through this several times with DIS equipped GM cars. Get a plug tester, and see if you don't find your car is running on 4 cylinders rather than 6...keep in mind, each coil fires TWO cylinders, so when a coil goes bad, two cylinders are missing. I used my plug tester at the coil packs and all look to be firing consistantly. when I just touch the throttle linkage at the throttle body there is a stumble then pick up right off the throttle stop. I will back probe the TPS when I get a chance but dam that thing is kinda crammed in there. Quote Link to comment Share on other sites More sharing options...
mra32 Posted February 6, 2011 Report Share Posted February 6, 2011 I had no trouble doing mine actually. It should be the same for you. What might have helped me is the safety pins i have taped onto the end. it is small enough diameter to fit into the back of connectors and the springy part allows many angles. Since I have 2 sets of test leads for the multimeter i have, I might solder or braze on the safety pins for a more reliable connection and less hassle with the tape. I think i replied to another thread you had and you seem to be going through the same things I am. However in the last 2 days my car has been running very well. I really dont know what caused it, but here are some things that changed: -I got gas from a gas station I dont normally go to on thursday (Sunoco instead of wawa). -Friday morning going to work, my car started to misfire under load, said screw it and just drove to work anyway and it cleared up halfway to work -Checked the code and it was the MAP sensor. This made total sense since I broke the plastic vacuum line to the map sensor and rigged up an assortment of hoses and tees and everything to replace what I broke. I checked on it before I left work and all was normal. -Friday night I made a more robust replacement of the vacuum hoses. Didnt notice anything. -Saturday night my car started running alot better. It was very wet out. -Sunday my car continues to run well even though its sunny and dry. Quote Link to comment Share on other sites More sharing options...
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