Engine will sometimes not rev
 

So I got this annoying problem, it does't happen often but it's annoying. Sometimes when I start the car (91 FC) it doesn't want to rev past 2k :dunno:, just bounces off the 2k mark. It isn't temp related because it happened with cold and engine and warmed up engine. Any help would be appreciated.

how is the idle when this happens? does it change? idle lower, lumpier etc?

I didn't pay much attention to idle when it happened, but I believe it was normal since the engine didn't want to stall

Any Check Engine Light?

If so, what are the codes?

If no CEL, when was the last time you changed the fuel filter?

The check engine light is never on, and even if I check codes by grounding the test connector it doesn't say anything. I didn't get a chance to change the filter yet since I had the car for not even 2 weeks. If the filter was bad wouldn't the problem occur every time, or it gets clogged and then unclogged by itself?

Does your CEL come on for a few seconds with all the other idiot lights during the self-test before you start up? If not, the bulb might be bad or missing - suggest checking that first, fix as necessary and re-checking the error codes.

The CEL does come one during self-test, than disappears and never blinks to throw a code

Does shutting the car off and the restarting fix the problem? If so, maybe ECU related (NO CEL, but still in limp mode). If not, how does it hit 2,000 rpm? Does it rev fast to 2000 and then just bounce, or does it rev slowly? Does throttle position have any bearing on it?

Shutting the car off is the way I always "fix" it. It does rev slow and rough/bumpy till it bounces at 2k. If I give it throttle where it would normally rev to 5k it still bounces off.

I have to think that it is an ECU limp mode thing. I don't understand why the CEL is not getting set. It may be something with the position feedback from the OMP (that is the usual culprit).

Try unplugging the IAT sensor while the engine is running and see if the CEL comes on. I am pretty sure that it should.

I will try it, also want to drive around wait for it to happen and do the self-test while its happening since every time it happens I'm not close to my house and don't have a spare wire.

Still didn't get a chance to check the codes, hopefully my car will break down soon :cuss:

LOL try unplugging the AFM plug to see if the stays running with it unplugged. And your engine light should come on.

Wouldn't that disable his fuel pump?

That is why I always do the Intake Air temp sensor, it is easy to unplug and doesn't cause any major harm to run without it. (You have to have a warm engine).

You can unplug the TPS too (I just tried it, it will throw a code too).

I'm thinking the OP is having wiring harness issues. Corrosion and heat exposure after 20+ years can cause intermittent opens/shorts in your wiring, causing all kinds of problems.