Hey everybody,

I have a 1990 Pickup v6 4wd with 150k and shes never given me a problem really... till now, ugh.

When i have the brake pedal depressed it sounds as if its going to stall, but always catches itself and stays at an even idle. The bogging almosyt sounds as if theres a heavy draw on the electrical system (IE if you were to let the clutch out to fast and its near stall, low RPM, yadda). Though the lights dont dim, radio doesnt cut out, basically everything is fine.... other than the engine sounding as though it will stall.

It only happens with the brake pedal depressed, in neutral, and is very inconsistent. It might happen just once at a stop light, or it may be every other second. Never completely stalls, and as soon as i let go of the brake and have it in first and pull away all is well.

Just put in new plugs, and wires. Also a new alternator with the last 10k. I have an optima yellow top battery as well.

Hoping you guys can help me with a diag. and help me correct this.

Thanks Everybody.

 

Check the brake booster. http://personal.utulsa.edu/~nathan-b.../3checksan.pdf (page 7).

If there's a leak, you'll end up with a big vacuum leak, which could (should) kill the engine.

 

Thanks for the reply scope.

The engine doesn't ever die completely, and is intermittent but always sounds exactly the same. A quick dip in the RPMs and the right back to normal idle.

I'm going to check all my vacuum lines this weekend just to make sure and thank you for the helpful PDF as well.

Another thing I'd like to mention is that if the truck is in gear and I have my foot on the brake (IE slowing down in gear) the intermittent RPM dip does not occur. Would the brake booster issue still occur in this circumstance?

Thanks again for your time, TRULY appreciate it.

-Ty

 

You mention a clutch, so it sounds like you have a manual. In that case the engine can't intermittently slow down while you're coasting in gear - it's locked to the rear wheels and has to maintain the appropriate rpm for your speed and gear.

I think scope is right on with the brake booster leak. Follow up on that and let us know what you find.

 

remove the vacuum line from the booster and plug it off, a finger will work. then have someone else hit the brake pedal and see what happens

 

I wish people posted their progress.