Weird engine trouble... Need help...
 

Yesterday I drove the car to work. It ran great. I fueled the car up to the brim. Then I drove the car to do a few errands. I got on it a little in third and it pulled smoothly. I put the car in neutral and coasted to about 20mph. The engine came back down to an idle. When I gave it gas again the engine would sputter and stumble almost like when you hit the rev limited only this was happening at around 2k rpm.

I gave it a little gas and the motor would slowly rev up to about 2k rpm and then it was like it shut off until it got down to 1k rpm. It would repeat this cycle over and over again. Luckily I had a little speed so I put it in 1st gear and cluched the engine up. Once it got to about 3k rpm it ran great.

After work I took the car to a good test road. As long as I don't get on the gas too hard the car runs great all day long. The first time I get on the boost and the engine falls below 2k rpm thats when the dreaded sputtering starts. So I checked all of my hoses, and connections, and vacuum lines I could get to and they all looked fine.

I tried it with 5psi and 15 psi and the engine responded the same to either boost setting. Also, the engine does not shut off when it is doing the sputtering thing. It idles just fine. It just will not rev above 2k rpm. If I push the accelerator to the floor it starts back firing a little. Also, if I get on the boost and keep the revs above about 3k rpm it runs just fine. I just can't get on the boost and let it go down to an idle or I will have to give it a minute or so to get past the sputtering stage. Surely this is a sensor problem or something easily diagnosed.

My mods are:
Huntley Racing MAF
HR Stage 3.5 Turbo
HR Hardpipe Kit
HR Monster BOV
Turbo Back Exhaust
Apexi Boost Controller

Any help would be greatly appreciated. :confused:

It sounds like your throttle possition switch (TPS) is stuck. The other thing I would look into are the connections at the back of the engine, where the speed and reference sensors connect to the DME. If they are loose you will get sputtering, but it would be a lot less consistant as a stuck TPS. Hope this helps.

Im new here, you might try to loosen your gas cap. The vent might be plugged. When you filled up there wasn't enough volume in your tank and it pulled a vacume. Worth a try and is free

Thanks a lot guys. I'll try those today after work. Let you know how it goes. I've had two other people tell me it's probably the tps. I hope that's it.

UPDATE:
I unplugged the TPS and the car runs a little rich but the stumble was gone. I plugged the TPS back in and it returned. I guess it's a new tps for me. Thanks a lot for hte help.

good to hear it was something fairly simple.

Yup, mine did exactly the same thing. Was able to drive around fine with the TPS unplugged. New one will fix that problem.