1998 Corvette
130k miles
The early C5’s have a 3-wire MAF and a separate IAT sensor.
They also have a separate Throttle Actuator Control module, being one of the first throttle-by-wire implementations at GM.
I was driving the car a while back (when it was owned by a friend) accelerating moderately (not floored), and around 55mph, it died. Shut off. Quit running. Coast into the nearest driveway kind of died.
Can’t recall the code that it threw back then, but I ended up disconnecting the IAT, and it ran well enough to get home. New IAT, it seemed to run ok for a while and then died again.
Seemed ok with the IAT disconnected. Of course, this points to not being ok in MAF, but being ok in speed density.
Occasionally, when driving with the IAT disconnected, the car will cough. Don’t know how else to put it. It’s not a misfire, not a backfire, it’s a cough as if the ignition was shut off and immediately restarted. Like one “pbth” from Speed Buggy and then it keeps going. Once in a while it’s sustained for maybe a second before it catches its breath and keeps going.
Once it came into my household, as my son’s car, it would die like this periodically when in MAF, and it was throwing a P0101. MAF code. Car had an aftermarket intake with oiled filters. Easy peasy. The oiled filters fouled the MAF as they usually do, right? Cleaned and then replaced the MAF with NO CHANGE. It was also throwing a P0113 IAT code at some point so I replaced the wiring harness at the IAT, and the wiring all the way back to the ECM to rule out an intermittent wiring issue. NO CHANGE.
Fast forward and I’m taking data with my cheap bluetooth scanner and Torque PRO.
Steady speed @ 50-55 mph and suddenly the MAF suddenly spikes, as does the indicated throttle position. Then they fall as the car dies, of course. Interestingly enough, you can clear the code(s) while driving, and it starts back up until it gets mad again.
Throttle and MAF spikes seem weird, since the MAF and the throttle signals should be independent, in different modules. The throttle is into the TAC, and the MAF is into the ECM. TAC wiring for reference:
www.lsenginediy.com/wp-content/uploads/2015/02/215.jpg
The data rate is too slow to see what’s leading/trailing. Is the throttle opening? Is there a coincidence?
Since
I have a 2001 Corvette, it’s simple to do a part swap. Throttle body and TAC swap between cars. NO CHANGE (though I do notice a different throttle response from the polished throttle body that was in his car when it went into mine).
So the car now has:
New MAF
New IAT
Known-good throttle body
Known-good TAC module
We went for a drive the other day and it’s doing the same thing. Dies with a P0101.
With the IAT disconnected I get a P0113 and P1111, neither of which are surprising.
Unfortunately, the ECM pin-out is different between ’98 and ’01, so I can’t do an easy swap to see if the gremlins have eaten the ECM. The car did live in a high-corrosion area (Florida gulf coast) before going to Texas, and now Michigan.
I’m frankly running out of things to point fingers at. (I have data with which to answer questions… I just need to find it)
Thanks!
Dave
