Question-------------------------
Followup To
Question -
I have a 1989 Pontiac Grand Prix 2.8L. The car idles very rough and sometimes stalls. When I try to open the throttle even a little, the car dies. I've got good fuel pressure, good spark on all 6 cylinders, the Idle air control valve bench checks fine and seems to be adjusting okay. This car doesn't have a MAF sensor, it does, however, have a MAP, and a TPS sensor. What do you think the problem might be?
Answer -
Check the MAP vacuum line for a crack in it and or it may be extremly soft and upon acceleration it tends to suck the line flat thus causing NO vacuum to the MAP sensor. Hand check the complete vacuum line or simply replace it with the EXACT same inside diameter vacuum line. If you install a smaller inside diameter line, you lose vacuum QUANTITY.
Next would be to test the TPS. A faulty TPS will sometimes NOT turn on the CHECK ENGINE light on the dash. You need to hand test it with a digital multi-meter.
If you do not know how to test it, Say so, And i will tell you how. This is a VERY delicate test procedure that you do several times to make sure that it is operating correctly. ONCE is NOT enough. Sometimes it takes 3 or 4 or 5 times to spot the fault within the TPS.
This is the most common 2 problems that frequently appear for this problem.
let me know and don't be to proud to ASK for help. You can't learn unless you ask WHY and HOW things work.
autohelp
New Mexico
Autohelp - First, I'd like to say thank you. This was the best tech support I've received so far. I put in a new MAP sensor and checked all the vacum lines. Still didn't fix the problem. I then went to the TPS sensor and checked it this was way: There are three wires going to the TPS; A, B, & C. I have a good 5v reference voltage from the ECM at points A & C. I then backprobed the connector between points B & C and got 0.5v with throttle closed. I slowly opened the throttle to WOT and the voltmeter smoothly rose to 4.1v at WOT. To me that looks like a good TPS. What next? I'm at a loss. If I have good pressure at the fuel rail does that mean my fuel pump is good? Do I need to block the return fuel line to see if the pressure rises to approx 75psi? What about spark? I've had a bad coil and a bad ignition module before in this car, but it didn't act this way. I'm desperate to get my car running but I just spent $1300 to have my transmissiom rebuilt and really dont want to take it back to a mechanic. Again, thank you very much for your help.
AnswerAfter you bench tested th IAC, You did reset it per manufacturers specifications BEFORE you re-installed it ?.
Are you using an ANALOG or a DIGITAL meter to do your tests ?.
You should be using a DIGITAL.
Let the vehicle set overnight and check the resistance of the IAC/MAT against the CTS they should be pretty close in ohm's value. If NOT, Replace the CTS.
Put some extra long leads on your TPS so you can put the digital meter on thedash right in front of you so you can watch the voltage changes from a COLD start all the way up to normal operating temp as you slowly accelerate and de-celerate the gas pedal.
once you reach normal operating temp, take it for a ride and watch the TPS to see if you get an erratic reading at some point.
You may want to also wiggle, slap and tug and yank at the engine electrical harnesses while monitoring the TPS.
Let me know.
autohelp
