hesithesitation upon acceleration and excessive strain cutti

[markykarky96]

I have a 1998 astro rwd and I replaced the engine transmission engine mounts fuel filter tune up distrubutor egr valve camshaft sensor gearbox pittman arm power steering pump hydro boost the differential ignition control module injectors and I'm suresureore just can't think of the rest now. When I accelerate slowly the car takes off normally but if I tap the gas peddal pr take off a tad fast they car stumbles/hesitates/hard shake. Its very annoying and if I but 87 gas its worse I have to use either 89 or 93 in order for the shake amd stumble to be better. No one has pinpointed the issue yet and its so annoying. Please help. Oh and the mpg's are suffering also and if you slowly take off and then pick up speed tue car clunks hard and jerks. I'm sure this is an air fuel problem but am just stumped as to what it can be.

[chevymaher]

Check the knock sensors. Being octane related sounds like they are freaking out when it is pinging. Going from normal to full knock setting without a transition in between.

[markykarky96]

How do u check the knock sensor?

[chevymaher]

Unplug them and drive it. If the problem goes away you know one of them is bad. Then try driving with one in then the other to locate the bad one.

If it rattles while your driving with them unplugged your having a predetonation issue for some reason. Causing the knock sensors to react.

Timing to far advanced or running to lean. Causes detonation. Or lack of octane, required by the engine, in the gas.

Knock sensors signaling knock causes timing to be pulled way off causing massive power loss. Stumbling, coughing in the engine.

If nothing changes when they are unplugged then it time to look elsewhere.

[redfury]

Also, if you changed all those things all at once or in quick succession, you may want to disconnect the battery posts and touch them together to discharge the capacitive memory in the computer so it can relearn the way you drive. Some sensors require that in order to run properly due to the computer previously trying to compensate for a bad component(s). Mahrer has it right though, it's something messing with the timing. That could be a knock sensor, a bad crank or cam sensor/sensor position ( which you say you replaced the distributor...was it aligned by a shop or did you just stab it back into the original spot as close as you could?)

[markykarky96]

thanks and i just replaced the knock sensor and the shake is some what better but the hesitiation is still there. i did take the posts and touch them together and that did nothing for it. the gas mileage is much better (got 115 miles for a quarter tank with a/c and leaving car on in lot with a/c for atleast 20 min). im just really stumped as to what can be wrong! im at my wits end with this car. and yes the dealer installed my distributor.

[Sailing_Faith]

Boy, that sounds like classic egr valve. It seems like you said you changed it, but I am wondering if you might want to try to make a block off plate for it and see if that changes the problem.

A folded aluminum can made into a gasket works well for this test.