Front end groaning and jumping at idle

[snocross1985]

OK, I have 2 problems with my truck right now. First problem is that when I am in reverse and apply the brake or turn the wheel I get a loud groaning noise. It will do it only in reverse and only if I turn the wheel or apply the brake, or both.

I also have a problem where at idle, in drive, and with my foot on the brake my truck feels like its gonna take off from underneath me. Almost like I am being pushed from behind. It is intermitint and surprises me when it does it because if I am not holding the brake down har, it can lunge forward a little. Could this be a vaccum leak? I'm really not sure on this one.

 

[snocross1985]

bump

 

[peties3]

Sorry, this has got me baffled!!! I wonder if your motor mounts are broken?
Mark

 

[snocross1985]

anyone got any clues?

 

[unpredictable1]

I also have a problem where at idle, in drive, and with my foot on the brake my truck feels like its gonna take off from underneath me. Almost like I am being pushed from behind. It is intermitint and surprises me when it does it because if I am not holding the brake down har, it can lunge forward a little. Could this be a vaccum leak? I'm really not sure on this one.

I've seen this prob on other vehicles - where the throttle body was gummed up and the plate was sticking open a bit resulting in constant partial throttle. Start with the easy stuff first.

 

[vrytired]

I also have a problem where at idle, in drive, and with my foot on the brake my truck feels like its gonna take off from underneath me. Almost like I am being pushed from behind. It is intermitint and surprises me when it does it because if I am not holding the brake down har, it can lunge forward a little. Could this be a vaccum leak? I'm really not sure on this one.

mine does this as well, so does my roommates 96 jeep grand cherokee. i've always figured it was normal in automatic transmissions? i figured it had something to do with torque multiplication or some other kinda of fluid dynamics that i don't understand.

 

[snocross1985]

bump...

 

[snoborder42]

sure it should want to move a little, thats the way an auto works but if you feel like you won't be able to keep it stopped. That isn't normal. Try cleaning the throttle body like lbrowne said and see what happens.

 

[chakaD]

Remove the black plastic cover over the throttle linkage and spray it with some wd-40. I have had three fords that have had this happen. The springs just get weak or rust up causing the throttle to stick open. It can be hair raising if you don't expect it. Adding an additional return spring can help as well.

 

[snocross1985]

OK, my throttle is not stuck open. The other day while I was actually being observant, my idle is around 500-550 rpm's while stopped and in drive. Is this low? I thought I remember my idle being around 700-800 rpm. If i give it a little throttle and keep the rpm at 700-800 while stopped and in gear it idles smooth. It seems that the truck is stumbling at the idle and giving me the jumping problems. Any clues on this one?


Also the front end crunching is driving me insane. It would make more sense to me if it did it all the time, but it only does it in reverse so I am baffled. Could this be balljoints or some bushing in my ttb front end?

 

[snocross1985]

bump

 

[Maniak]

The IAC is what tries to lift your idle. If the IAC is bad, the idle won't come up when the a/c is turned on (to keep the idle the same speed) and you won't have one touch starting (you have to hit the gas a little to start it) and it wont' run when cold out (idle)..

If the TPS is bad (jumping voltage) it will confuse the computer and your idle may bounce around, which will make it fun when sitting at a light. There are a couple threads around here on how to test the TPS. Basically, you are just trying to watch the voltage the TPS is showing at idle and while the throttle is opened. I believe it should be .96 volts when closed and should raise smoothly as you open the throttle (There is a thread about free hp which talks about adjusting your TPS).

The other think I can think of is the posibility that you have a vacuum leak between the brake booster and the engine. Move around that vacuum line when the truck is running (in park) and see if the line is caught or rubbing against something. I've seen it where there was a vacuum leak, but only if the line moved. The fitting of the line as it went into the booster was bad.

~Mark