Alright for the past week or so of driving the car I have noticed a wierd reving problem. The car, while in drive and while braking almost to a stop with randomly rev. But enough to where if I'm on the brake the tires will almost start to spin. I put a new battery in the car about a week ago and when I first started if after it reved high. I thought the car was just reprogramming or what not. I went out to grab an xmas present today and coming to a stop light it did it. I was then stopping to pull into my driveway and it did it again.
Is this the sign that a sensor is dirty or starting to fail? Car is an 88 bird with an 87 5.0 motor from a bird.
Rev as in how high? From your description it sounds like it's revving and not stumbling which means it's getting extra air from somewhere (vacuum leak?). Other than that, I can also think that the transmission isn't downshifting properly, causing it to go into a lower gear than it should, causing the engine to rev up but this shouldn't add power to your rear tires.
why not pull your codes?
i agree on the vac leak thing,, do you have auto brake release?
your describing a lurch or lunging forward and could be dangerous.
I only had this happen once and it was due to my CFI base plate gasket was cracked thus sucking air,,ie- vac leak.
Vacuum leaks or TPS. I would still pull codes. The computer will tell you.
Auto brake relase? You mean the lever thats part of the dash for the e brake? I checked the tps, well I cleaned it and so forth.
The lurch or lunging is what I am describing, and it is dangerous.
It seems to happen when braking, just as I am about to come to a stop. Maybe a leak in the master cylinder? Anyway to check it?
some cars came equipped with auto brake release, meaning when you have the emergency brake on,, as soon as you shift from P to D, the emergency brake automatically disengages.
No, I do not have that. My ebrake is actually disconnected at the moment regardless.
spray carb cleaner around various vac connections to include the intake mating surfaces to the heads. listen for an rpm change. dont forget to spray along vac actuated solenoids.
next up would be the tps like haystack siad.
do you understand how to test the tps?
Alright this problem has reappeared. I was not able to find a vacuum leak, and the random engine revving has returned. It does not matter whether the car is in park, nuetral, or drive, randomly the engine rpms will spike. In traffic this is especially problematic. Any other suggestions? Besides the TPS, would any other sensors potentially cause this? I tested the TPS when this problem started, and it was right on the money.
I just re tested for codes, and I got a code 29, anyone know what this means?
best i can find is the vss (speed sensor)
try the MAP sensor. I had the same problem with my cougar... checked everything, replaced all the gaskets, the tps, everything... the MAP sensor has no way to really test it except when it goes bad. on my cougar, it was a black box mounted on the driver's side on the firewall right behind the intake. just a thought.
What I don't understand is that if this is truly revving up, the motor would run rich, stumble and want to die unless it is getting adequate additional air. No sensor will give you more air but it can make the idle air bypass open up to feed it a little more oxygen. Without air though, the engine just can't/won't rev - it's the stronger, more rapid combustion that makes rpm's increase (outside of downshifting transmissions).
I say disconnect the idle air solenoid's connector, increase the opening of the throttle body a little bit, and see what happens. If it's happening in park, pop the hood and see what's going on around the throttle body. Something this simple may tell you everything.
If all's well at the throttle body, then it's a vacuum leak or funky shifting of the tranny.
the MAP sensor, if it's not working, will cause the computer to think there is not enough air pressure in the system, which will cause the engine to open up and pull more air through, which causes the revving up. that's what happened with my cougar. it would rev up in the drive thru and the person at the window would think i was trying to impress them with my sweet ride...
What do you think is "opening up"? The EEC's got control over the IAB, not the throttle body. Only your foot and cruise control have control over the TB. The IAB is a very small, and turbulent, bore.
i'm just relaying what my mechanic buddy told me. just trying to be helpful because that is the exact problem I had, and replacing the MAP sensor fixed it.
I'm curious - did that show up when codes were pulled? I would think this one would be caught by the eec.
mrtrembl1,
What year is you're car? Did you just buy a new MAP?