Hey guys I am totally stumped by this truck. Its a 99 blazer ZR2 that has problem after problem after problem. I bought it from a shady guy who told me none of these issues and of course it drove fine until I paid for it. Anyways it all started with a stalling engine, misfiring and terrible gas mileage. I took it to a local shop where they saw the last owner put in Autolite plugs and they said it won't run well unless delcos are put in. That made a big difference but it still was running rich and occasional misfires. At that point I got a code for the engine temp sensor, replaced that and the misfires were gone. I thought all was finally well right? WRONG. Got more codes about a "too rich condition" so I took it to the shop again. Turned out the fuel pressure regulator was bad and the spider unit was also bad. $900 to replace that and finally the gas mileage improved and the rich condition was gone. Well the next day on my way to work the engine light comes back on. This time it is throwing "idle air control" code. I thought maybe it was the sensor on the side of the throttle body so I unplugged it and the engine began to idle very high so that tells me that the sensor is fine because as soon as I plugged it back in the engine leveled back out. At this point thats where I am at, and occasionally the engine is hesitating on acceleration( the rpms will fluctuate back and forth for no reason causeing the truck to lurch back and forward slightly). That only happens occasionally though. I drive it a half hour later and it runs great. ??????

So far on this truck the catalytic converter has been replaced, o2 sensors are functioning properly, fuel pump is running strong, new cap and rotor, new plugs, new EGR, new map and tps sensors, new spider, new fuel pressure regulator. I don't know what else to do??????? Any help out there?

 

If you did not change the plug wires, change them also.

Pull your throttle body off, disassemble and clean out all the carbon. In particular where your idle solenoid inserts, and the back side of the throttle plate.

Another item is the MAF sensor. I had a really bad stumble on my 96, and one of the things I did (besides plugs, wires, cap, rotor, TPS, cleaned throttle body), was to disassemble the MAF sesnsor and VERY carefully cleaned the crap off the elements and the inlet/outlet throats.

After I did all of the above, runs like a new engine and 16 city 20 hwy mpg with 125,000 miles and no oil consumption.

 

Sounds similar to what my 97 was doing. I only found the real problem by running a live data stream with my code reader while it was acting up. I would SERIOUSLY gather more information before you spend either time or money on solutions that dont solve your problem. It turned out it was a bad sensor shorting to ground intermittedly. Good luck!

 

My Blazer may be doing the same thing. Hesitation while accelerating and occasionally at cruising speeds but only after the car warms up. Still hunting for the problem. Not quite ready to give up and take it to the dealer.

kristoph30, what sensor was shorting on yours?