Engine won’t rev above 1500 rpm.

[yundar]

Hey guys back with another stumper. This one is on my 87 944 NA. The car starts and runs just fine. It’s even drivable while it’s cold. As soon as the engine warms up however it cuts out and dies. Well not quite fully dies as when I coast to the side of the road and the rpms fall below 1500 it starts right back up again. It seems to run fine at the lower rpm. In fact the last time this happened I was able to drive home at 1500 rpm or less and the car continues to run like this, just won’t rev up. I replaced the DME relay and even tried my jumper wire just for kicks. Runs the same either way. Per Clark’s Garage I was suspecting the throttle position sensor. When I test it with the multimeter I get the correct readings or at least close. I never get to Zero ohms when the switch is in contact. The best I can do is about .7 ohms on both the off idle position and the full throttle position. I am assuming this is just residual resistance in the switch. Should I really be able to hit zero ohms? Is this too much resistance in the switch? What other things might cause the car to die at above 1500 rpm and only when warmed up? It is very consistent and it is definitely shutting off as opposed to coughing and sputtering but still running. Not sure where to look next?
Thanks, Andy

[LambInLionOut]

have you checked the AFM barn door? the clark's garage instructions give details of it's operation.

Air Flow Meter (AFM) Operation and Testing

[yundar]

I have not checked the AFM. Symptoms don’t exactly match but I can run through Clark’s test procedure tomorrow and see what I get.

[yundar]

Ok I have checked the AFM as per Clark’s. Everything comes up normal in the process except for checking the intake air temp sensor where I get an open or infinite reading. According to Clark’s this would indicate running rich but plug inspection seems to be normal. I am getting a little frustrated as all test from both Clark’s and the factory service manual seem to indicate the car is ok yet it still won’t run above 1500 rpm when warmed up? Anymore ideas or has anyone else experienced this problem? Thanks, Andy

[djnolan]

Does the same problem occur if you rev the engine when not driving, and did you say it revs fine when cold? Shooting in the dark, you could also check the fuel pressure per Clarkes, and also test the DME temp sensor. Could be a clogged exhaust, too. Or a DME or coil going bad or even a crank sensor going bad. Need more definitive symptoms.

[yundar]

Yes the same problem occurs when I’m not driving. In fact that’s how I figured out I could drive it home. It will start and run and even drive it just won’t rev up. I was able to limp it home by shifting before 1500 rpm into each gear. It does seem to start and run fine when cold for example first thing in the morning. I have just replaced the DME temp sensor. I have not had a chance to test it in the car as it is still disassembled from testing the throttle position sensor and the AFM. Both of these components test ok. I guess I’m not suspecting the two regular DME sensors due to the fact that the car runs fine under certain conditions. They are not the original sensors and were replaced a last year. Same with the fuel pressure regulator. I have not tried to test the fuel pressure under the malfunctioning circumstances yet.

[yundar]

Also exhaust is brand new this spring from cat delete test pipe back so reasonably sure it’s not clogged.

[yundar]

So a bit of closure on this one too. After going through all the usual suspects and testing everything I was doing continuity tests of the harness back to the ECU. I noticed a burn mark on the pin that is the ground for the computer. Since the wiring harness still had continuity for the ground I suspected the computer must have had a short in it at some point. I live in a damp environment and sometimes things just get wet. Long story short I sourced a replacement computer and now the car seems to run fine! Thanks for the suggestions!
Andy