Strange problem around 1600rpm in 1st & 2nd

[Blk95gs]

I have a 95 TSi AWD manual. I am trying to figure out what could be causing this issue.

If I am in 1st or 2nd gear, and let off of the throttle, the car will almost not let me smoothly hit the accelerator pedal, and then when it finally seems to recognize that I am hitting it, the car jerks really violently. Now I know that my motor mounts are bad (they're in the mail) but what would cause the problem with the throttle.

PS. I slowly revved the car (about 5% throttle) up to 1600RPMS earlier, and as soon as it gets there, it bogs down to idle RPM (about 800 RPMS) Is that a sign of any sort to a certain problem? It's done this since I bought the car back in Sept, and it was stock then.

Thanks.

 

[femmeDSM]

Have you thought about plugs/plug wires? Sometimes it really is something that simple.

Do you have a logger, or access to one? Maybe posting a log would help us see what's going on at ~1600rpm. Also could be a bad boost/vac leak (like, really bad)...

I don't know exactly what you mean by "it bogs down to idle", I'm assuming that it just doesn't like reving past 1600, and the rpms will just go back down immediately? I'm a little confused on that part.

If this was happening in my car, I would check the following: plugs/wires, coil, Boost Leak Test, ISC/IAC, TPS, run a good log, and get voltage readings on all related sensors.

 

[Old Mitsu Tech]

I'd look at the tps, If it is glitchy, it freaks out the computer.

You can use a scope as I don't think most multimeters respond fast enough for glitch capture.


I know, I know, scopes are hard to come by but, they are almost a necessity.

Or, you can try a known good component.

Good Luck

 

[Jackyll]

your problem sounds a little bit like mine so I thought I'd post here too...

mine's kind of doing the same thing but it does drop back down to idle rpms, and it does it whenever i lift off the gas or get on it... but only at light throttle. Like if i'm slowly letting off the gas from 10% to 0%... or slowly getting on it from 0%. I replaced the TPS already since it needed to be, and that's what brought out this problem because I didnt' notice it before. It doesn't really happen when the car's cold though... only after it's warmed up. Feels more like lag though, so I will be doing a boost leak test as soon as it gets warmer then 10* outside... wish i had a heated garage .

 

[Blk95gs]

Ok, sorry for not replying at all to this...I only have the internet at work, so no access on weekends.

Have you thought about plugs/plug wires? Sometimes it really is something that simple.

I did check them, thinking possibly the same thing, but as I have just replaced the stock units with NGK BPR6ES and Magnecor 8.5mm wires, nothing seemed to be wrong in that department.

I don't know exactly what you mean by "it bogs down to idle", I'm assuming that it just doesn't like reving past 1600, and the rpms will just go back down immediately? I'm a little confused on that part.

Sorry for not being more clear. It was only if I gave it a SLIGHT bit of throttle, then at that point, it would just go back down immediately as if I had let off the throttle, then rev back up like nothing happened. All while I was maintaining the same amount of pressure on the throttle.



One thing I did notice while weaseling around in the engine bay was my throttle cable had A LOT of slack in it. So my first attempt was adjusting the throttle cable, which rendered to be kinda tedious. It seems like it may have fixed the issue, but I also noticed that there was a a relay up against the firewall in the center of the car (there's 2 of them bolted there) that was clicking. LOUDLY. The vac hoses from the TB seem to be routed to this. The clicking went away after I adjusted the throttle cable though. Sorry for being vague, I do know my way around these cars somewhat, just never had to pay attention to certain things

 

[femmeDSM]

Sorry for not being more clear. It was only if I gave it a SLIGHT bit of throttle, then at that point, it would just go back down immediately as if I had let off the throttle, then rev back up like nothing happened. All while I was maintaining the same amount of pressure on the throttle.

This sounds like TPS to me, as Old Mitsu Tech mentioned earlier.

I also noticed that there was a a relay up against the firewall in the center of the car (there's 2 of them bolted there) that was clicking. LOUDLY. The vac hoses from the TB seem to be routed to this.

Once again, TPS is a likely suspect. The TPS is located on the throttle body, near the ISC.

 

[Blk95gs]

Seems to be the consensus. I'll likely be replacing that to see if it further remedies the issue.

Thanks for the info.

 

[Jackyll]

Don't know if you're still checking here, but I'll post anyways

As I said in my first post I already replaced the TPS, and that's what brought out my problem similar to your's. All I had to do was adjust the TPS. It was off by a hair so it only studdered at light throttle. I adjusted it and the studdering went away. But now I have another problem ...

 

[femmeDSM]

But now I have another problem ...

....Ahh, DSMs....Gotta love 'em. Haha.

Story of my life.