1992 Buick Lesabre periodically accelerates during low-speed braking?

I'm glad I found this site. Hopefully the members here can help me with a perplexing problem.:banghead:

Periodically my 1992 Buick Lesabre tries to accelerate while I'm braking at low-speed. This is a very intermittent problem. I've taken the car to my mechanic and he's tried disconnecting the cruise control, which didn't help. He also replaced 2 control modules on the brake pedal. This eliminated the problem for several months but it has started again. The mechanic didn't find any trouble codes in the car's computer nor did he find any re-calls for this problem so I'm at a loss.

Any ideas as to what may be causing this?

Thanks.

This could be a leak in the power brake booster, an idle air control (IAC) problem, or throttle body sticking. Have you tried to tap the accelerator quickly & let off, when this condition exists? Are you sure that the application of the brake pedal is the cause of the higher idle speed, or is the idle speed high when you apply the brake? A good way to test this, is to put the car in neutral, take foot off the brake pedal and observe the engine rpm’s when this happens.

Another possibility is a vacuum leak through the brake power booster. The additional air admitted to the intake will increase engine RPM.

Thanks for your help. The problem only seems to occur during braking when the car is going 30 mph or less. The motor revs up to about 3500 rpms or so. If I take my foot off the brake and back on quickly it goes back to normal idle. I think I tried to touch the accelerator once, but this happens so infrequently that it takes you by surprise and have had to use both feet on the brake to stop.

I forgot to mention the throttle position sensor (TPS) as a possibility here. Do you have any codes?

The last time this happened was about 5 months ago, and there were no codes shown. The car is about to go back to the mechanic and scan it again. I will be taking these postings with me. Thanks.