Lately my GTA (5.7 TPI) has been acting up - the idle is pretty rough, it seems down on power, and has a bad off-idle hesitation when you accelerate normally. The stumble isn't really apparent if you smash the gas or come off the stop gentley. It also started sputtering, especially when I go around a corner - as I accelerate the thing seems to die and I have to get off the gas and it comes back to life. I also just checked my mileage and it has dropped from 17-18mpg to 9mpg.

Not good. I installed headers/exhaust over the winter and brand new AC plugs and Accel wires. The cap/rotor isn't too old (also Accel), and neither is the fuel filter, about 2 years. I don't have any codes.

Any help, thoughts, suggestions appreciated

Thanks

Eric

 

sounds to me you have two problems. First the TPS==throttle position sensor could be bad, that will cause the car to hesitate when you step on the gas.. Second ... the only thing i could thinks of about bad gas miliage is the o2 sensor. but unless i miss my guess, that should set a code to the computer.

have you replaced you wires lately, I would check those first. If they are worn, it could be that the wires are bad, and are getting a weak spark.

 

Well since you said that you replaced your wires recently, the're probably not worn, but I would still check them to make sure none of them are barbaqueing on your headers. Also makes sure they are tight on plugs.

Tom

 

also make sure your plugs are tight...they do back out sometimes.

 

Don't overlook a possible EGR problem. Most of the symptoms you describe are consistent with the EGR system. If it is a TPI getting to the EGR valve is a problem because the intake runner is in the way. The valve is controlled by a vacuum solenoid under the ignition coil. Check lines etc.. Many times the valve itself gets clogged with carbon deposits and it won't shut all the way. LOL, Dan

 

I had the exact same problem on a non third gen car once, but the tubing from the map scensor to the engine had rotted in half. Horrible gas mileage smoked black, smelled rich and ran like sh*t. Check that!

 

Thanks for the replies. The wires are all tight and good - the ones that run close to the headers have heat shield sleeves around them to protect them from the heat. I have thought about the EGR also but because it is such a pain to get to I have been avoiding it. If I were to replace the EGR valve does it come complete? Or is the solenoid a separate piece? And how can I test either of them.

There is no smoke, at least none that I can see, and the O2 sensor is brand new - installed with the headers.

The hesitation off-idle is not new, but the rough idle is recent, and the crappy mileage just started in the past couple weeks.

More thoughts??

Thanks again

 

dont the tpi's have coolant temp sensors just as tbi's?<---not sure about that one. Dosent that cause all the symtoms mentioned too? Just tryin to help by throwing that out there..

Brandon

 

Yeah they do. Something to check, but an inactive CTS will most likely throw a code. Check out the tech articles on this site for detailed explanation of EGR operation and troubleshooting.

 

Sounds to me like a vacuum leak. Check your vacuum, should be around 16-17inhg on a stock L98. If you have a way to check you o2 voltage do that also. It should change from high to low very quickly at idle and be around .8 or so at WOT. Keep an eye out for the vacuum leak being on the passanger side runners and or the driver's side intake manifold gasket. If you rev your car in park or neutral does it backfire? Decent way to see if you are running rich besides the crappy gas mileage.

 

where is the best place to check the vacuum?

 

The best place IMO is on the plenum, but I guess the intake itself or the TB would work. I personally use the FPR fitting to test.

 

I tend to think that neither the EGR, TPS, or O2 sensor is the problem because you said you're not receiving any codes. As is my experience, the Check Engine light will come on before you start experiencing any problems. Just a thought, though.

 

The same thing is happening to my car. When I start it idle rough and sometimes cuts back off. when I step on the pedal the rev isnt steady it putters untill around 25 or 30 rpms. It would usually go away after I drive for 2 or 3 miles. I thought it started when I filled up at a cheap gas station, could this have anything to do with the fuel system?? its an 88 Iroc 305. any hep is appreciated..

 

Installed headers over the winter did ya? I installed headers on my car with some supplied gaskets that the baastards at flowtech sent me. They took all of a week to start leaking. Long story short, this leak alone took me from over 20 mpg to around 10 mpg! The bad news is that an exhaust leak is dammn tuff to find, and it's no fun to change the gaskets if you find one.

I new this was happening on my car when I found my BLM's going well above 128 under any type of prolonged load (highway driving). Sounds to me like a scan tool will benifit this situation regardless of the problem at hand.

Good Luck

 

Have you checked your fuel pressure for consistancy?

 

How do I check the pressure???