Tony89

Someone's bound to have had this happen, so I hope whoever has finds this thread, here goes. My '89 tuned port started bucking and stumbling about 3 weeks ago. It set the TPS "voltage too high" code. After replacing the TPS and ECM, no improvement. In a "last ditch" effort to address the problem, I put in a remanufactured mass airflow sensor that I got a deal on a couple of years ago. It fixed the problem.....for a week. Last week Tuesday, the symptoms returned, but this time, NO CODES. It had run well for that week, but now, it's back to running like crap. In the "start with cheap, go towards expensive" tradition, I raided my spare parts box. I replaced: (1) the relevant fuses, (2) the MAF power and burnoff relays (I believe), (3) the coolant temp. sensor (it's just as easy to replace as it is to test on a TPI car because of its location), all to no avail. I tested the analog and system grounds (for the sensor) with the dark green signal wire and got 5.0 volts. I tested the red power feed wire from the relay, and got battery voltage. I tested the "D" connector "in run" to see if the burnoff relay was leaking voltage into the system, it was "0 volts" so it checked out OK. Finally, I checked the signal voltage "in run" an it read 4.2 volts AT IDLE!! Yikes. It spiked even higher when I revved the engine. I checked out the fuel system two weeks ago, and it was fine. Could my replacement (refurbished) MAF sensor have crapped out already? It seems unlikely, but the high voltage at idle points to this, and I'm flying blind because I still get no codes. Any input would be appreciated because I really don't want to have to buy another MAF sensor. My paranoid sixth sense says "buy new" but that is a lot of money to drop when not absolutely sure. Thanks for any pointers.

irocbadboy

check your oxygen sensor!

Red Devil

Seriously doubt it's the MAF. I tend to lean towards leaking injectors or bad CTS for these generally. Have you tested f/p and leakdown time? Inspected the FPR? Have an AFPR? Was the CTS a known good one or one just sitting in your box?

Tony89

Thanks for the responses. The CTS was a known "good" one. It's brand new. The thing that leads me toward the MAF sensor is the really high voltage reading at idle. 4.2 volts is an acceptable wide-open-throttle number, and both of the grounds and power feed are fine. I changed the original MAF sensor with the reman. unit two weeks ago, and it ran fine for a week. Then, the same symptoms came back. If the injectors were the culprits, the MAF wouldn't read that high. The 4.2 figure goes up as I rev the engine. It's almost as if it catastrophically failed. Its calibration seems to be off by 90% or so. The cherry on top of this whole "crap sundae" is the fact that the car still isn't setting any trouble codes at all. Just to clarify, when I purchased the "new" MAF a couple of years ago, I did it for the specific purpose of removing the screens and gutting the heat sink. I removed the screens, but never removed the heat sink. I then read all the material about how the screens really need to be there, and replaced the intake side screen with a larger mesh. Is it possible that the adhesive that I used to attach the new screen destroyed the hot-wire element? I checked the fuel pressure during the original diagnosis, and it checked out fine. If it had been something "mechanical" like a torn diaphragm, the voltage signal of the MAF would be reading "normal," so I ruled that out.