1991 chevy 350 tbi poor throttle response

[348tripower]

Can't seem to locate the problem. If you stand on it it runs good. Ease into it and it takes for ever to respond. Good smooth idle. Converter fell off a few miles back. Advance seems to be working as shows when setting timing and pluging the wires back on.

[enjenjo]

Check the throttle position sensor with a miltimeter, the resistance should change smoothly from idle to wide open without any jumps or dead spots.

[348tripower]

Ok. He said he has changed it but it could be defective.

[348tripower]

220,000  timing chain?

[wayne petty]

sounds like when you have it running ... that its running in closed loop as it should....   when you accelerate... at a normal pace.. that it just does not respond...  but when you mash the throttle....  it drops out of closed loop... and into open loop where it runs a preprogrammed fuel and timing setting..


i am taking that you don't have a scan tool..... to look at the live data stream...

a few things i would dive right into.....

http://www.fastbird93.com/diagnostics/lacking.jpg
or

http://www.fastbird93.com/diagnostics/Hesitation.jpg

more here...

http://www.fastbird93.com/Diagnostics.htm   the info on this site.. is for gm. LT1 motors with the distributer behind the water pump...  but much of the other info is exactly what you need to diagnose each circuit...

look at the bottom left.... all the way down... the MAP sensor output check..

http://www.fastbird93.com/diagnostics/MAPOutput.jpg

you might want to unplug it without tearing the nipple off the bottom.. verify the hose is clear to flow ... no restriction.. check the passage into the intake or back of the throttle body...  it should have manifold vacuum on it..  ..

does your truck have an air injection system...    there is a diverter valve...    there are 3 sections where the air is controlled into...

diverted to atmosphere...

down stream air.. into the exhaust pipe just before the cat... or into the side of the cat....

upstream air...   the upstream air is injected into the exhaust manifolds right at the exhaust ports...    this can only be allowed to happen when the engine is in open circuit...  when its NOT setting fuel mixture by looking at the oxygen sensor readings...

once in a while... a check valve in the air injection system will rot out...   or some other problem that causes the diverter valve to allow air into the upstream all the time... this can really fool the ECM into doing weird things with the fuel mixture...

i normally pull the hoses off at the check valves...  plug the opening on the check valve  so no air can leak in.. then start the engine..  you will probably have to plug one of the hoses you have unhooked to be able to tell if the system is switching properly... with just a finger over the end of the hose....

other charts you might want to check out...
see if you can force codes... by following instructions..

codes  14, 15, 21 , 22, 23, 33, 34,

look at 44 and 45...

do you need an exact wiring diagram for the engine...

i would also like you to check the grounds... either behind the cylinder heads..  or near the thermostat.. but if it runs good when you hammer on the throttle.. it is probably one of the above..    either restricted map sensor hose..  or air leaks into the upstream air...  

you should print this chart...   please ONLY LOOK AT THIS CHART ONE LINE AT A TIME...  



you will also need to make a set of test leads that have clips to pierce the insulation on the wire without damaging it...



notice the teeth...