3

(Solstice)

So, I cleaned my throttle body with brake cleaner. I thought it was carb cleaner, but I am apparently illiterate. (Honestly, I'm not sure what the difference between them is.) I was very careful not to get anything on the throttle control / sensor connector (one connector, electronic throttle).

When I put everything back together, I started the car, and it ran pretty well, though it was rough for a few seconds after starting.

No CEL, but I read the DTCs anyway and got:

0x7E8: P0107 - Manifold Absolute Pressure/BARO Sensor Low (Pending, Current)

(And the MAP reading in HP Tuners is flat, no variation whatsoever.)

Idled for about 5 minutes, revved the engine, and it stumbled and died. I pulled the codes and got a new one:

0x7E8: P0068 - MAP / MAF - Throttle Position Correlation (Pending, Current, Old)

Started the car again, stumbles and tries to die. Clear codes and, voila, it runs smooth again, but still has the MAP error. If I rev it up, it stumbles, dies, second code (MAF) comes back, and stays that way until I clear the codes.

Wash, rinse, repeat.

I'm a fan of consistent, predictable behavior but, sheesh - WTF?

Oh, and I looked at one of the logs from this morning before I cleaned the TB, and the MAP was working fine at the time. :( I wiped it down before plugging it back up, everything was dry. And now I'm stranded out of town until AutoZone can get a new sensor in tomorrow, for the low price of 100USD.

  • Carb cleaner is more aggressive that brake cleaner. Did you remove the sensor and clean out the air port? Getting cleaner on the connector end will not usually hurt the sensor but getting cleaner and dirt in the air sensor port can. – Fred Wilson Feb 11 '17 at 22:36
  • @FredWilson the sensor is mounted to the manifold. I removed it after this started. I cleaned the throttle body off of the car. I haven't tried blowing out the sensor port, but it had zero variance in the voltage output, which implies that it's not doing anything at all(?). Verified continuity in the harness with a multimeter. – 3Dave Feb 12 '17 at 0:29
  • If the sensor air port were plugged then the sensor would read the same regardless of manifold pressure. I may be failed, that is, however very uncommon. Hence the reason the parts store does not have it in stock. In my 30 years fixing cars I have replace only a few and all of those were damaged in cleaning or mishandled. – Fred Wilson Feb 12 '17 at 3:26
  • @FredWilson ok. I'll try blowing it out, though that's not easy (GM 2-bar MAP, just a hole which I assume has a plunger on the other side). Fortunately, "stranded" is a family place with every tool, but it is 30 mins to the nearest gas station. Thank you for your time. – 3Dave Feb 12 '17 at 4:19
  • @FredWilson I replaced the MAP, no change. Now looking at wiring. I don't see a fuse for this thing anywhere, could be missing it. – 3Dave Feb 12 '17 at 17:07
1

The problem was the harness.

On this car, there is a short "injector harness" which drives the injectors and the MAP, and is separable from the main engine harness. A solder joint near the MAP sensor connector was flexing and causing an intermittent signal path.

I had another injector harness with an incorrect MAP connector, so I cut the connector off of the first harness, Western Union-spliced it into the other harness, soldered and heat-shrink wrapped it. Everything is working fine now.

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