What is the relationship between braking and rpms? A few weeks ago I was driving on the interstate and all of a sudden my car starts sputtering (like fuel starvation), backfires, goes into erratic rpm action, and dies. Although I was able to restart it, this sequence was repeated, and I eventually had it trailered home. When I restated it the first time on the interstate, I noticed the ABS light came on, and stayed on w/ each restart. Turns out the Opti was bad and we changed it. In addition, we installed a new fuel pump (Walbro 255). However, residual problems remain. Not only does it now idle rough (like surges) when I first start the car, when I hit the brake pedal, the rpms drop significantly and the car almost dies, especially when it is in gear. When I release the brake pedal, normal rpms are restored to normal if I am in nuetral (A-4). Initial thought is the brake booster is bad so I plan to have it replaced. Also, there are no codes showing on my scanmaster.
Questions:
1. Are there other possible problems (ie bad sensors, etc) that might be at work here?
2. Would the bad booster cause the ABS light to come on and stay on, even after PCM reset? 3rd tailight is working, btw.
3. Could the backfiring, etc. during the Opti failure be related to this? In other words, did the backfiring, etc cause other damages that are manifesting as these symptoms?
4. Could there be a relationship between the new fuel pump and the idle issues? Fuel pressures are fine, although pressure drops to zero immediately after turning off the engine (another issue that needs attention). BTW, at WOT it runs fine.

I appreciate any insights you may share.
Thanks!
Mike

 

probably a vacuum leak.

 

Could it possibly be a problem with the torque converter?

 

anytime you have problems with the motor and the brakes, the first thing you do is check vaccum. a vaccum leak at the motor will make it idle harsh (harshness varies from mild to wild). also, the brakes draw certain amounts of vaccum...period. So if you have drastically low vaccum, the brakes will still draw what it needs to operate properly so the engine will get whats left of the vaccum. Since this is not a high pressure ABS/brake system or a hydroboost system, the chances of the problems being related are 90% or so. Now, if the computer finds that there is not enough pressure to operate the abs system fully, it will then disable the ABS system temporarily. This often happens during giant burnouts, donuts, and some other things. good luck. lol

 

Check for vacuum leaks and put a vacuum can on it.
Ya didn't say how big your cam is??

 

I had a simular problem with my car, but being speed density it would idle high with a vaccum leak ESP when cold. Any time I would hit the brakes it would surge. I insalled a new booster and that fixed the surging problem, and lowered the idle down a bit. BTW it was the biggest PIA with the engine in the car!

But my car still surges when put into gear or taken out, and I think that is torque converter caused