Algot

I've read all the threads on the rough idle problems that people have had. Since then I've tried just about everything: plugs, wires, fuel filter, air filter, pcv valve, numerous vacuum hoses, fuel pressure regulator, engine temp sensor, i've checked the plugs for possible fuel injector leaks and checked the EGR for proper functioning.

It seemed to have been fixed when I replaced the FPR, but two weeks later, the problem returned.

It happened when it was warm, and when it was cold, now it seems to only happen after it's warmed up.

this is driving me f'n nuts

any ideas?
please?

Thanks

simon kenton

What brand spark plugs do you have?
Did you clean the throttle body?
Did you change the Oxygen sensor?

Warped

I'm not familiar with the 91 and my 87 doesn't have it but, does your truck have an idle air control valve or something similar? That'd be what I suspect.

Algot

they're autolite plugs
O2 sensor has not been changed
and the problem arises when i'm decelerating

simon kenton

Spark plugs ok.
Change oxygen sensor.
Clean throttle body.

Dwntyme

It's possible tha your slackside timing chain guide is broken causing irractic timing...

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lincolnnellie

Definatly sounds like your O2 Sensor...

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Algot

ok, so i changed the o2 sensor
and taking a hint from another forum, checked the back pressure transducer (BPT)
I found a vacuum hose that I had missed, it practically disintigrated in my hands, so I changed that.

Problem solved..........almost.
while it had been coughing the black smoke and sputtering for a while
now it's taken to hesitate oh so slightly on deceleration at a much smaller frequency.

my guess is that either the BPT or the EGR valve is to blame
any thoughts?