just picked up a 91 rs 305 tbi and it has some hesitation under load. prime example is to ease into the gas with the bake on. the motor breaks up a bit.

what are some key things to look into on this?

 

Is the gas old or maybe have some water in it.
Check the timing.
Just some suggestions. Matt

 

gas is fresh, no leaks and new fuel fitler as well. have not replaced the pump but it's a low pressure system so i would assume the pump is fine since it does start up and drive ok. timing is a few degrees advanced 2 or 3 at most.

 

I dont know, but I think my throttle shafts are worn out on my car and it whistles and idles high for a while before idling down. This happens at every stoplight. At about between 2000-2500 rpm it hesitates in each gear and I guess what I am leading to is a vacuum leak could be a prob.

 

Unplug the two wire electrical connector from the EGR solenoid. Now take it out and drive it around. I am willing to bet your hesitation disappears. You might even be able to duplicate the feel right now by raising the RPM up to about 1200-1500 in Park/Neutral, after several seconds it will start missing heavily. The cause is typically a bad EGR valve, well not so much bad, but the bypass passage becomes plugged with carbon. The passage is so small going up through the valves stem that it is almost if not impossible to clean. When the passageway clogs, the valve is now pulled open much too soon. Another way to test that the valve is working properly is to start the car, let it warm up, then feel the backside of the valve as you bring the engine up to a constant 2,500 rpm or so. You should feel the diaphram start rapidly cycling up and down as it "meters" the exhaust gases to the intake. When the passageway becomes clogged the valve will simply pull all the way open and cause the bog.

 

i know mine seems to do this more once it's warmed up..?

 

Could be a bad 02 sensor. They often go bad and do not throw a code. This would explain a hesitation when in closed loop.

 

THANKS FAST!!!!!!! My old mans 5.7 truck did this right after he bought it. It baffled me because the valve moved freely and everything looked good visually. I just plugged it because he doesn't drive it much and I didn't want to spend money on something that might not fix it. It turns the SES light on at cruise and freaks him out, eventhough we know the cause. He will be very happy with an easy fix.

 

I have a '91 TBI L03 and it has vacuum only going to EGR, is there some way else I can test that to see if it's the problem. Also, any ideas regarding how to isolate an intermittent vacuum leak? I have something funky going on under there but have no clue what's happening. All started with the new EGR, but I suppose it's working becasue the EGR stopped throwing a code... 'bout ready to say f*%$ TBI and slap a carb on there!

 

So many things... Faulty/worn spark plugs, bad ignition, low fuel pressure... Have you done a tune-up yet?

 

throttle shaft bushings wear out after 50,000 causing a vacume leak and unsteady idle. have them serviced

 

never heard of these before. where are they located, couldn't i just replace them myself or is it something i have to have rebuilt?

 

Teh throttle shaft wears into the TBI housing. The main problems it causes is a throttle that sticks open. The only cure is to have the TBI housing bushed, which requires machining.

 

ah... i see.

i'll have to look into that.

 

had exact same problem.... TIMING! Check base timing!!

 

been there, did that... unfortunately. thanks though!