Low Idle and mid-range hesitation issue (1 Viewer)

[crispy21]

Working on my 1994 80 Series with 265k.

Been battling a low idle when engine is warm and a mid-range hesitation/stutter when holding speed and not accelerating. Also has a weird lag during acceleration when on the engine temp is on the cooler side but as the RPM's build up to around 3,000 the old girl takes off like a rocket.

I have replaced the spark plugs and dizzy. Both O2 sensors replaced. EGR Vacuum Modulator just replaced. MAF and TB gate cleaned.

Don't know what direction to head to next.

Any advise?

Thank you,
John

 

[Davidl890]

Any check engine light?

 

[ColoradoBoy]

Have you gone thru all of your vacuum connections? I recently removed my throttle body and gave it a good cleaning (was running high idle); one of the small ports was completely clogged. After cleaning and run-in, my idle settled back down to normal. It's amazing to me how a plugged 'pin hole' can affect the whole system. I spent a lot of time chasing the high idle/hard-to-start-when-hot last year. Your symptoms sound like vacuum issues(?)

 

[crispy21]

No check engine light at all. Very frustrating that it will not trip anything. My local shop smoke tested the vacuum system and found no leaks. But if it is clogged that wouldn't show. I will look at them.

 

[bajaphile]

What I'd do ...
Have you gone through a full tank of gas? Make sure its just not a bad/old gas.
Check intake hose, especially around the bellows for racking. Check vacuum lines as already mentioned.
Check PCV.
Check fuel pressure.
Generally these engines don't have issues with the idle air control valve, but its not unheard of. If you remove throttle body to clean, try cleaning the IACV. (Be careful with the brass philips panhead screws).

 

[crispy21]

Thank you. I have run a few tanks with injector cleaner and one with dry gas, in case I got a bad tank. The air intake hose is newer and is solid.

I learned a hard lesson on those screws for the IACV.

The battle continues.

 

[Harry Orme]

Thank you. I have run a few tanks with injector cleaner and one with dry gas, in case I got a bad tank. The air intake hose is newer and is solid.

I learned a hard lesson on those screws for the IACV.

The battle continues.

Hey mate did you end up solving this issue?

 

[Tayoflor]

I've got a 1994 80 sitting in my driveway with the same issues. Im about to pull the trigger on a new VAF sensor.

 

[Kentex Rick]

Been chasing a slight miss on my 93, I have a small exhaust leak, been wondering if that is causing it. Going to change out exhaust manifolds for newer style and delete the pair system, just waiting for new gaskets.