'87 ciera needs a choke

[m1782t]

2.5 TBI acts like an old carburated engine with the choke not working, will start but dies in drive, starts back up in park and dies again in drive. If I let it run with a little gas over idle it misses until it warms up then will usually run fine. New fuel filter, new kit in TB, fuel pressure keys up to 12 (spec 9-14) starts runs and holds 12 the whole time. TPS measurs right values for close and open and perfectly linear in between. New IAC valve, coolent and air temp sensors, also new Map sensor. No codes and no air leaks I can find, the only other odd thing is that the fuel pump will run for up to 3 seconds after the key is turned off. Where to from here?? thanks.

[maxwedge]

A full scan and look at all those sensor inputs, also tap the pcm firmly with a screw driver handle and see if anything happens, engine shudders or comm is lost on the scanner.

[m1782t]

Well guys after some severe medical setbacks, I'm back to this project. I put it on an analyzer after sitting inside over night, the water temp sensor said 62 the new mat said 242 and when the mat was unplugged it said 306. I had tested the old mat and it was right where it was supposed to be at -10, 70, 210, but I replaced it anyway. This left only the wiring and the pcm. Since wires don't get better than new when they fail, I replaced the pcm, no help. I unplugged the mat and clipped a 100k resistor to the leads, so it would think it was -40, still no help. It still thinks the engine is always warm. Can the prom on the pcm loose it's settings and can a new one be purchased, or the old one tested or reprogrammed. Is it worth a try to put the one in from the replacement pcm which came off of an 89 Calais? Or is there something else that would make the pcm think the mat is always hot? thanks

[autojoe]

air temp thermistor unplugged should show -40 on scan tool.is this 3.8l engine?tan and black wires at mat?check the mat signal wire tan wire from mat to ecm for a short to ground.disconnect the mat connector and with a voltmeter pos hooked to harness tan wire and neg hooked to black wire key on engine off you should read around 5 volts.best way to find a vacuum leak it with propane.....i would unscrew the end piece of a small propane attachment for plumbing and hook the vacuum hose to it and run along intake gaskets ect and listen for rpm change.carb cleaner will work but can catch fire.i used to do propane while monitoring the 02 on a scan tool to see if it goes rich.since then i bought a smoke machine.
fuel pump runs after key is turned off?does it run for few seconds after key is turned to on position?with key turned to on position is the check engine light on for bulb check?

[m1782t]

2.5 engine, Mat wires are yellow and black/pink. I do get 5 volts accross the leads. However, today I did get an engine light after getting it started and warmed up. Codes were 23 (mat circuit problem - oh really!!) and 35 (iac/fuel pressure) the iac and tps have been replaced and the fuel pressure was fine last year when I checked it. My guess is that 35 was generated due to the 23. After 3 back surgeries I don't bend too good so will have to get someone to trace down the wires. Do the leads go directly to the pcm, or is there something else in that circuit? Also yes the fuel pump does run a couple seconds both when you key the ignition and after the ignition is turned off. thanks

[autojoe]

code 23 low temperature signal voltage high...either open signal wire or open ground.if you got 5 volts between mat signal wire and ground key on engine off....signal wire and ground wire good.maybe this code set when testing the mat circuit with disconnected....there is a voltage sensing circuit inside the computer.code 35 sets when actual idle speed is 300 rpm above or below the desired idle speed for 50 seconds.does the idle hunt up and down?check mat connector?clear codes and see if they return......key on engine cold after sitting all night coolant temp sensor and mat should be fairly close in temp reading on scan tool.with mat plugged in backprobe the tan/yellow signal wire with key on engine off engine cold....you should have a reading between 4-4.5 volts.....hook negative meter to negative battery terminal.what is your idle rpm?hows the plug wires?spray with water and see if it misses.

[m1782t]

Got a little time between snow storms - checked vacuum lines with both propane and carb cleaner and found no leaks. Misted the spark plug wires with water and no miss. Idle does not hunt, and Mat has been replaced. Cleared codes and after 4-5 minutes it gave a code of 23 again. My next step is to cut into the leads of the mat and pcm and run wires directly, if this sounds reasonable - are the leads connected directly or is there anything else in between? thanks again.

[Tech II]

What I would do, disconnect battery....disconnect the ECM.....measure your resistor on an ohm meter,,,,,attach the resistor to the harness of the MAT.....now measure the MAT circuit resistance at the ECM harness connector and compare....

PROM'S can't be programmed......doubt they are available anymore....or are hard to get....

[m1782t]

Tested the new MAT and it's identical to the old, both are right on specs. I do have 5 volts at the MAT connector with key on engine off, also 5v from tan wire to ground. I put a small resistor (185.6) accross the connector and found 184.0 across the wiring when tested at the ECM, 1.6 less resistance is probably just a cheap meter, at any rate no increase. No path to ground on either wire. Code reader still thinks it's 242F when the engine is cold. Runs fine after getting it started and warmed up. Still getting 23 code, but check engine light turns on for a few minutes then off for a few minutes, and repeats. Thanks in advance for any ideas.