bucking and hesitation

nw_91_4x4 · Mar 8th, 2006, 05:03 PM

My 91 pickup 4cyl has developed a frustrating problem. After the truck has been warmed up for about 15 minutes it starts to buck and hesitate on deceleration and light load. If you accelerate it's fine. Randomly, at idle it hesitates, but hasn't died on me. There's no tach, but it seems like the idle speed doesn't drop off right away at idle.

My mechanic adjusted the fast idle cam and the idle speed. He's also cleaned the air flow sensor.

What else should should we be looking at?

dvdswanson · Mar 9th, 2006, 02:02 PM

check the TPS and IACV

79kz400 · Mar 10th, 2006, 12:57 AM

Some members report this problem relating to the fuel filter clogging. Replace and repost.

chud · Mar 11th, 2006, 10:01 PM

How do you check the TPS and IACV? Would the check engine light come on for those problems? I have a similar problem I'm trying to figure out.

Thanks.

nw_91_4x4 · Mar 16th, 2006, 09:44 PM

Quote:

Originally Posted by dvdswanson

check the TPS and IACV

New IACV and Thermostat element. Problem solved.

nw_91_4x4 · Jun 15th, 2006, 02:32 PM

My hesitation is back. :-(

Cold start fine, once warm, it starts to buck while declerating (revs fluctuating). At idle the revs jump around. Goose the gas... it drops to normal idle.

Anything else I should check?

dvdswanson · Jun 26th, 2006, 11:26 AM

Quote:

Originally Posted by nw_91_4x4

My hesitation is back. :-(

Cold start fine, once warm, it starts to buck while declerating (revs fluctuating). At idle the revs jump around. Goose the gas... it drops to normal idle.

Anything else I should check?

check the TPS

alm350 · Jun 27th, 2006, 01:56 AM

i would check to make sure you have good fuel pressure, and replace the fuel filter, could be the egr valve is sticking, if your loosing power when this happens and it smokes a lot, also check the maf, or it could be that the iac you replaced may have gone bad again, it happens trust me.. keep us posted

hellion111 · Jul 12th, 2006, 02:52 AM

Quote:

Originally Posted by nw_91_4x4

My hesitation is back. :-(

Cold start fine, once warm, it starts to buck while declerating (revs fluctuating). At idle the revs jump around. Goose the gas... it drops to normal idle.

Anything else I should check?

Try disconnecting your O2 sensor and driving it like that for awhile. If your hesitation and buck goes away just replace the sensor and all is well. If not it could be a bad tps or perhaps plugwires or spark plugs. The tps failure is not easy to test however. Generally what happens after time is the tps wears out at an area where you do your most cuising, say 35 miles per hour as an example. You might also have an egr valve that is partly stuck open causing egr flow at the wrong time. A plugged catalitic converter can cause the egr to open at the wrong times aswell. Let me know how you make out.