I'm having some rough idle problems, and have tried TPS, Fuel Pump, Plugs, Wires, Cap & Rotor, & Ignition Control Module(had old one tested, tested bad). Also did PCV, Fuel Filter, Fuel Pressure Regulator(not the whole spider assembly), Air Filter, and the oxygen sensor on the exhaust pipe right before the Converter. Is there another oxygen sensor that I don't see? Some people say there's only1, some say 2. which is it? it has obdII connector, but not sure if it's actually OBDII. Also, the only code showing up is P0122(Throttle Position Sensor). Replaced it twice, pretty sure it's not actually that. Checked all the wires to it as well, no apparent problems. Fuel pressure holds pretty steady around 60 (even left it overnight, and it was still good). It sometimes runs smooth with the TPS unplugged, just at high idle, but sometimes low idle where it's real rough with the TPS unplugged. Also get black smoke when it's running rough. No smoke when it's smooth at high idle, though. Really confused here. Any ideas would be great. Thanks in advance

 

First place the model year and make in your signature so that we don't have to guess as to which year you have. It does make a bigdifference to how to diagnose a problem. Some years came with CPI and most with CSFI and the newer models from '02 on had LS1 style spyder...

Check the MAF, EGR for dirt and carbon (EGR) and clean as needed. EGR will require new gasket...you can even get one with a screen to reduce carbon build up in the EGR...

Also if there is a lot of carbon in the EGR valve and passages then check the TB also, especially the IAC (Idle Air Control) valve. Carbon can build up in these areas and cause bad idle.

Plus run some fuel injector cleaner through the system like Chevron's Techron or Seafoam...you could have a fouled poppet. If so depending on the year the Dealerships can replace the old poppet style with the newer LS1 style "spyder", it reduces the risk of a sticking poppet causing idle issues...if it is not under warranty it will cost most of $400 US but is replaceable by the mechanincally minded shadetree mechanic...

Good luck hope these suggestions help...

 

he said he swaped out the spyder already, not sure if they would do the popets at the same time.

i think you should look at your egr(exhaust gas recerculation) valve and see if it is working.

does the problem only happen after the engine has warmed up? or is it only when it is cold?

 

It's a 95, 4.3, 4-wheel drive, Vin W. I have done the Fuel pressure regulator, not the actual spyder unit. I haven't really had it running long enough for it to warm up, one thing i did notice is that when i pop it into gear....well, in drive, it's the same, but in reverse the erratic goes away and it kicks into high idle but is a lot smoother. EGR is clean....it was dirty, but didn't have chunks of carbon or anything. it's all cleaned up now and has a new screened gasket just in case. and by check the TB, i assume you're talking throttle body? everything has been cleaned up, i've taken most of the vacuum hoses and checked them for leaks, none found. everything seems like it's in working order. And it seems to start up fairly easily, but half the time it dies right after starting(within 5 seconds) it takes a few times before it will actually run, and crappily at that! I even tried starting it up with the electrical connector for the EGR unplugged, and it was smooth at low idle for maybe 30 seconds, but then acted the same as i've been describing.

 

Well after doing some research you may have the CPI version for that year and when you replaced the regulator did you look at the fuel lines going into the spider??? These are plastic and if they are disturbed they might work correctly ie: Leak on the drivers side causing rough idle etc...and you may not have a MAF sensor if you did it would be located between the air filter and the TB there would also be an IAT (Intake Air Temperature) sensor in the air tube between the MAF and the TB...

Also your TB (throttle body) would be different than my 2000 Vin W engine. It is located on the front of the intake facing the radiator...

There is also a possibility that the Evaporative Emissions purge solenoid is not working properly or you have a canister that has filled with excess gas from overfilling the gas tank.

Also there is a MAP (Manifold Absolute Pressure) sensor in the intake to measure vacuum inside the intake to tell the computer how much air is flowing into the cylinders...

 

Well, my former 95 had a gas leak in the intake and black smokes. You may want to look tru the valve hole located there. Remove the valve and with a flashlight look for bright spots and gas smell inside the air intake (only air should be there). In my case was the regulator but the hoses there are prone to leak. This excess of gas is sent in the air into the chamber and the sensors/PCM can adjust it. You mentioned that gas pressure may stay overnight, but ....

 

ok....can anyone explain this to me? i was looking at the wiring diagram in the haynes manual, and noticed the engine coolant temperature sensor was connected to the throttle position sensor. unsure of what it would do, i unplugged the coolant temp sensor, and the truck started right up, ran pretty smooth at normal idle. plugged the sensor back in, and it's pretty close, still have a slight miss, but it's definitely driveable. how could unplugging the coolant temp switch fix my rough idle?