Hey folks, new here I was reading the tech articles on this site trying to find out a odd problem I'm having with my 350 TBI, it's not actually a third gen, but a '91 fullsize Blazer, so I'm assuming the TBI systems are very similiar and maybe someone can shed light on this problem as I'm stumped.

Here's the major symptoms:
When engine is cold, the idle is pretty rough, the RPM's will get very low, to the point you're sure it's going to die, and then will just perk right back up a bit high and work back down again, and do this over and over until it's warmed up. After it's warmed up it runs pretty good.

Now the tricky part, after being warmed up and running good, if you shut it off for say just a few minutes and restart it, it runs like hell all over again, sometimes even worse than when cold. After just a minute or so, it runs great again.

Now after a few weeks of doing this, and not getting a code, I finally got a code 22, and it became more and more frequent as time went on, so this weekend I finally replaced the TPS sensor, code went away, but problem persists. I also cleaned the EGR and IAC, with no apparent change.

I've had no luck finding anything with this symptom both cold and hot when restarted, any clues?

 

I would have deff thought EGR....or a bad Vacuum leak somewhere

 

I thought it was the EGR as well since I cleaned the one on another car a couple months ago and it ran like new again. Mine was barely dirty.

Another thing I noticed, if I stick a can of Seafoam or other fuel additive/cleaner in the tank, it runs pretty good. The injectors aren't dirty, I visually inspected them and they spray great, it's just something about having an additive in that makes it run much better, as soon as it's back to straight gas the problem comes back Anyone make heads or tails out of that in relation to my problem?

 

Unplug the vacuum hose on the EGR. Start the engine. does the problem persist? It sounds like it is definately running lean.

If it is still turning the SES light on and giving a code 22, check the TPS voltage with the Key ON engine OFF. Using a DIGITAL multimeter, it should read about 0.50 volts with a closed throttle and smoothly ramp up to about 4.5-5 volts @ WOT. I bet you will be reading near 0. Probably a wiring problem, most likely right at the TPS connector.

 

It stopped throwing the code 22 after I put a new TPS sensor on, and runs marginally better but still the majority of the problem persists. It does seem like a lean condition, occasionally from a stop if you punch the throttle it'll studder and backfire, I just cant figure out where the condition is coming from. O2 sensor was replaced shortly after this started happening, timing is set, can't find any apparent vacuum leak.

I'll try that EGR trick this weekend, should I plug the hose that runs from the EGR solenoid to the EGR?

Thanks for your suggestions and help fellas.

EDIT: Also whats the best way to get a fuel pressure reading with the TBI setup? I probably should test that this weekend, but don't know where to get a reading from.

 

Yes, plug the line.

The fuel pressure reading is a little hard to get. You need a special adapter that screws in between the fuel line and the fuel filter.

 

I see the parts houses have the Actron GM TBI pressure test kit, anyone know if you can get just the T with shraeder valve by itself anywhere, or what size it is? I hate to drop $40 for a tester I'll use once.

 

OK made a ALDL cable and ran WinALDL for a bit, heres some logs. Obvious thing is it's running rich, and in the 1st log, about 98 seconds into it, put it into reverse while holding brake and just died. Most of the things seem to be about right as far as I can tell, but they probably make more sense to you guys.

The Logs.zip contians both logs already saved in Excel format for your viewing pleasure.

 

If you still have the original hard plastic line with the rubber ends between the TB and PCV valve you might pull it off and have a look. Mine was split underneath near the TB and also had terrible part throttle performance (cold idle also a little rough but WOT always worked just fine). I replaced it with standard 3/8" vacuum line and the thing instantly ran much better.

Also check your base timing using the proper procedure. A/F stuff takes a back seat if the timing isn't close.