Hi everyone -

I have a 1991 Firebird w/ 305 TBI engine we just picked up. I am having an issue with hesitation -

When idle, the motor runs fine, no signs of miss or fuel issues. We have tested the fuel system, and it is putting out a very steady 10 lbs, which is on the low end of spec, but still in the 9-14lb spec. ...as a part of an attempt to tune it up (and hopefully eliminate this hesitation) we've put new plugs, wires, distributor cap and fresh rotor on the car as well as a fresh fuel filter. The hesitation issue remains.

Here is my best description of the issue -

When sitting at a stoplight or driveway, the car idles fine. Then, as you begin to accelerate like normal, it hesitates, loses power, but never backfires or seems to miss, and then as you get through about 1500-2000 RPM, it cleans right up and runs great. Additionally, you can go to WOT at almost any time with no hesitation, no stumble. ...once you get up to cruise speed and get back out of the gas, and you're cruising in that 1200-2000 range, you can feel the stumble once in a while (almost like a miss).

I started out thinking we have a fuel pump issue, but my gut tells me that the car would perform WORSE at WOT not better if that were the issue.

I'm now leaning towards the ECM or something ignition related. Anyone have any ideas? I'm going to cross post this in the Electronics section. I appreciate your thoughts.

 

Have you checked your timing? I had hesitation issues with my '88 when I first got it, checked and reset timing, ran better afterwards.

 

Could easily be EGR, or TPS. Might be other things as well.

As usual, ten minutes with a scan tool reading the data stream is worth more than two weeks worth of internet guessing.

 

It sounds like it could be the EGR. You can check this by removing the vacuum hose and plugging it with a small screw. If it runs good EGR delete, you have a bad one. If not you can rule it out.