The throttle position sensor only communicates the throttle position to the PCM. The IAC (idle air control) valve, also on the throttle body) controls the idle speed and possibly could be causing this.

 

OK, I had a chance to finally look at this car. I actually drove it to my house last night, what a trip that was. The Blazer runs OK at 3000 rpm or better, if you let it drop below that it wants to die. I was fortunate to have a highway nearby so I drove it on the highway, without using Overdrive. I made it home ok, but cornering was tough. I also noticed the brakes were very hard to push (either from the engine trying to die orpossibly a vacuum issue). I could not find a vacuum leak, but will look hardernext time. I will go to Autozone andrent an enginecode reader, the check engine light is not on (burned out?), but there has got to be a problemwith one or more of these sensors.

I also discovered that the fuel filter was not replaced, I thought it might have been when the fuel pump was replaced. I will replace that.
Any suggestions with these new issues found?

 

Hard brakes might be an indication that the brake booster has a leak. This would be a LARGE vacuum leak that would cause the engine to race. The first thing I would try is remove the vacuum line where it goes into the brake booster. If you do not hear a rush of air into the booster, then there is a leak. If it is just the check valve, then that is pretty simple, but I suspect it is the booster itself. Remove the check valve from the end of the vacuum line and plug the vacuum line with a large bolt. Start the engine and see what happens. If the idle is correct, you've found the problem. If not, then you've eliminated one more thing.

 

That's what I will do during my lunch break today, If the rain quits.

Thanks,

 

Well so much for that idea. I disconnected the vacuum line to the master cylinder. It has the same issues. My daughter heard back from the guy that replaced the fuel pump Today, he thinks the Catalytic converter is bad. I think it is something in or around the intake manifold. What are some indications of a bad cat?

Heres what it does if I just turn the key to start..It starts revs to 3500 rpm for 3 seconds and dies. It will restart but the same thing happens time and time again. I also believe the fuel pump may still be bad, the first time I started it yesterday (after sitting a week or so) I had to pour gas in the throttle body.

 

So you disconnected the vacuum line at the vacuum brake booster and plugged the end of it?

A bad catalytic converter usually doesn't allow the engine to rev at all. So if you were able to drive it, maintaining over 3000rpm, then your cat isn't the problem.

 

Yes, I plugged it off with grey tape, the check valve seems to be working correctly. I did find some severely deteriorated vacuum hoses, I cut off the bad ends put them back on. I will have to buy some more vacuum line to replace some of these.

It really seems to me to be a fuel issue, I think the fuel pump might not be generating enough pressure, or the filter is partially plugged. I just cant explain why it runs at high rpm but wont run under 3000 r's or how I was able to drive it 15 miles (highway) if it wasn't getting enough gas.

It's all too confusing for me.

 

did you make sure all the intake sensors like MAF are plugged in properly? i know if i take off my intake assembly the motor revs but then dies ad if i can keep it revved it will stay runnin. could just be me though

 

I checked these sensors and YES they appear to be hooked up properly.
I also picked up a spray can of CRC (HF) Contact cleaner, and used it to clean the MAF sensor (the 3 little tiny wires within). I put everything back together and re started the vehicle, NO change ..Starts revs to 3500 then dies. I then went to Autozone rented a diagnostics code reader, it says P0101 MAF or VAF A CKT (range/perf). I erased the code and started teh vehicle up several times and the code did not reappear, if it were bad, how much run time is required to get the code again?

Somebody told me to check the fuel regulator under the plenum, what this? Where's this? How would I go about checking this?

I'm still looking for answers

 

AH HAH !!!! The problem turned out to be a crack in the upper plenum. It went un-noticed because it was in the rear next to the distributor. I assume the engine must have back fired or something along the way. I am in the process of finding a plenum, so far I have only found one, it needs to be removed from a Astro Van with the same engine 4.3l Vortec. It looks like the same one, sure hope it works. I have a '96 Blazer, the replacement isfrom a '98Astro Van.
The crack wasabout a inch and a half long and very difficult to spot, the only reason I found it was when Inoticed teh seal wasn't setting flat and tried to push it back into the seal area.

Thanks everybody for there help, especially swartlkk