I have a 98 TA with about 56,000 miles and I did the MS4 and heads over the spring. I had a mail order tune done. I tran like a beast for like two weeks when it was all done. Now when it gets high into the RPM's around like 4,000 rpm it starts studdering and popping and acting all crazy. if it is just sitting it will rev above that all day (just rev'd to check). I have cjecked all the plug wires and they seem to be fine. I am thinking fuel filter since I have never changed it. Other opinions would be greatly appreciated.

 

yes fuel filter is good way to start , plus check up your maf sensor and check if you have any strange noises from the engine when idleing maybe you bend a pushrod or somthin.

 

The engine sounds same as before. I will start with the fuel filter though.

 

OK changed the fuel filter with no results. when I start it up I let it warm up for a few minutes because of the stiffer springs. when I first pull out onto the highway I get all over it and it runs awesome. After I drive in town for a few minutes (long enough to get to operating temp.) it starts running like **** above 3,000 RPM. maybe almost like a cylnder is missing. I will probably check the plugs and wires and after that I am lost unless it is something with the tune.

 

hmmm... i think you may have an oxygen sensor failuer < chek it up if you have HPtuner or go to any work shop who have a hyprotech hand held they can tell you whats goin on< i dont think its plugs and wiers anymore because the idle was smooth as you said, also it might be a crank sensor i rememebr we had a simillar problem before and it was the crank sensor failuer . so i think am leaning toward a tuning and sensors issue , good luck man and keep us inform

 

I have new oxygen sensors in and I'm not throwing a code so I don't think it would be that. Would a crank sensor throw a code?

 

yes it should throw a code but in some cases it doesnt . when its the last time you clean up your MAF ???
you said its start to run like **** above 3000rpm ,what exactly the car does?

and if you changed the fuel filter how about your fuel pump?? i rememebr i had a fuel pump issue before when i hit the paddle it will run great till it gets 4000rpm and above and the car will start to run like it want to turn off till i get my feet off then everything will back to normal ?.

 

It's hard to trust a mail order tune. I'd say what most likely has happened is that it's been running rich and now its finally bad enough that you notice. It has either fouled the plugs or o2 sensor. I'd check the plugs out and take it to a dyno and see what you're workin with.

 

Id get that thing on a dyno for a real tune, and have the A/F ratio checked.

 

That is kinda what I am thinking. I think plugs fouling is def. possible. Just haven't had time to mess with it lately. thanks guys.