Strange RPMs while stopping

dwd1985 · #1 02-28-2006, 12:57 PM

I just adjusted my TPS to EXACTLY .5 Volts. I thought this would fix one of my problems, but it didnt. As im coming to a stop, when im at around around 1000 RPMs, my RPM's will suddenly increase slightly (like by about 50), and the car will take a slight lurch forward, even though my foot is on the brake. It could possibly be while it is downshifting into first gear. It happens everytime I am stopping. But all of my other shifts are fine, including the upshift from first to second, so im pretty sure that it isnt a tranny issue (but I could be wrong). A possibly related problem is that when I am accelerating at low speeds, and then take my foot off of the gas, my RPMs will drop VERY quickly, and then suddenly come back up again alittle. However, driveability isnt affected at this time, its like you cant even feel it. Any ideas? I thought this was all TPS related, but I geuss not...

intelisevil · #2 02-28-2006, 09:23 PM

Is your AC/Defrost on? If so, the rpms will increase at idle, maybe that's what is happening. As the engine slows down to idle speed, the circuit kicks in to increase the speed.

This morning I was sitting at a stop light in Drive with my foot on the brake. I turned on the Defrost and the increase in idle (about 100 rpms) was enough to overcome the slight pressure I had on the brake pedal, I actually moved forward for a moment until I pushed on the brake a little harder. Fortunately, I was the first car in line, after a twelve hour graveyard shift my reactions aren't always the fastest . . .

dwd1985 · #3 03-01-2006, 12:08 PM

Quote:

Originally Posted by intelisevil

Is your AC/Defrost on? If so, the rpms will increase at idle, maybe that's what is happening. As the engine slows down to idle speed, the circuit kicks in to increase the speed.

This morning I was sitting at a stop light in Drive with my foot on the brake. I turned on the Defrost and the increase in idle (about 100 rpms) was enough to overcome the slight pressure I had on the brake pedal, I actually moved forward for a moment until I pushed on the brake a little harder. Fortunately, I was the first car in line, after a twelve hour graveyard shift my reactions aren't always the fastest . . .

It happens regardless of whether the AC/Defrost is on or not. Does anyone know what this could be? I have been troubleshooting this problem for some time now...

Earthworm · #4 03-01-2006, 01:38 PM

Does it only do this once per stop? Perhaps the AWD is binding? Try inserting the FWD fuse to see it the problem goes away.

dwd1985 · #5 03-01-2006, 03:23 PM

I just put in the FWD fuse, and it didnt change anything, so I geuss it isnt AWD binding. Any other ideas?

Earthworm · #6 03-01-2006, 03:30 PM

The FWD light came on right?

At what speed does this happen?
Have you ever verified the TPS is properly adjusted?
Will this happen with the shifter in different positions? (1,2,3,D)

dwd1985 · #7 03-01-2006, 03:38 PM

Quote:

Originally Posted by Earthworm

The FWD light came on right?

At what speed does this happen?
Have you ever verified the TPS is properly adjusted?
Will this happen with the shifter in different positions? (1,2,3,D)

Yes, FWD light came on.
It happens around 5-10 MPH
I adjusted the TPS yesterday to EXACTLY .5V (as stated in the first post)
I dont know about the different positions of the shifter, I will try that next.

dwd1985 · #8 03-01-2006, 06:17 PM

I tried driving around with the shifter in every different position. With the shifter in 1, I would be cruising at 10 MPH and 2000 RPMs, and then take my foot off of the gas, and it felt like someone slammed on the brakes, but the RPM's didnt change. After that, it was the normal weird braking thing with the shifter in 2,3, and D. So any ideas now?

Earthworm · #9 03-01-2006, 06:30 PM

So that's the downshift from 2 to 1.

dwd1985 · #10 03-01-2006, 07:14 PM

I geuss it could be the downshift from 2 to 1, but that doesnt explain that slamming on the brakes feeling that I got while driving around in first gear only. It also doesnt make sense that I have no other weird shifts, especially an upshift from 1 to 2.

dwd1985 · #11 03-03-2006, 05:12 PM

So I have thought about it, and the downshift from 2 to 1 could possibly be a problem, but maybe it is 2 seperate problems. If it is the downshift from 2 to 1, then that would by no means affect the fact that sometimes when taking my foot off of the gas pedal (when driving around 40 MPH and 1500 RPM's) that I take my foot off of the gas, the RPM's will drop by around 300, and then increase on their own back up about 200 (these are both just geusses as to exact numbers). So what do you guys think? 2 seperate problems or could both be caused by one thing, and if so, what could it be?

oab_au · #12 03-03-2006, 06:13 PM

Quote:

Originally Posted by dwd1985

So I have thought about it, and the downshift from 2 to 1 could possibly be a problem, but maybe it is 2 seperate problems. If it is the downshift from 2 to 1, then that would by no means affect the fact that sometimes when taking my foot off of the gas pedal (when driving around 40 MPH and 1500 RPM's) that I take my foot off of the gas, the RPM's will drop by around 300, and then increase on their own back up about 200 (these are both just geusses as to exact numbers). So what do you guys think? 2 seperate problems or could both be caused by one thing, and if so, what could it be?

I think it could still be related to the TPS. The TCU looks for the closed throttle signal from the TPS before it applies the over run clutch.

It would appear that the clutch is not applied when you lift the foot, so the rpms drop, till the clutch is applied to pick the rpms back up to road speed.

The action is different when the shifter is in 1st.

Harvey.

dwd1985 · #13 03-06-2006, 01:31 PM

Also (I cant believe I forgot to state this) at idle, when I first stop, I will idle at about 1000 RPM's for about 3 or 4 seconds, and then it will VERY SLOWLY creep its way down to 600 RPM's (which I know is the proper factory setting). So does anyone think that all of these problems taken together could possibly be a bad ECU? I think it is either the ECU or some weird TPS problem, despite the fact that the TPS is tested as good and adjusted properly.

19svx94 · #14 03-11-2006, 12:59 AM

have you tried simply checking your tranny fluid? also try reseting your ecu and see if the problem still persists before purchasing a new ecu

dmnknightomega6 · #15 03-12-2006, 02:31 AM

since we are on the ECU... Are all ecus the same throughout the year models? (soory if this is hijacking). My car does this crap too but only when its cold - engine wise like morning.