Thanks Rob180 - I've cleaned the EGR valve and it seems to be sealing fine.

Well I changed the plugs and tested wires.
All plugs have a light tan patina and minimal deposits. All plugs are very worn. AC541-932 with center worn down to a small point a some metal deposits on the electrode.

Wires ohmed out between .975k and 1.310k ohms. Shortest to longest wires. Well within spec.

Checked compression on all but #3 - I just can't get the tester on that cylinder, no room.

#1, #4, #5 - just shy of 145 psi
#6 - 130 psi - but I had a weak battery by then
#1 160 psi

spec says minimum 100psi and lowest must be at least 70% of highest.

Still have a rough idle. I have not yet put a scanner on to see if any change in readings.

 

okay guys - i still need some help.

The problem is a fluttering rpm at idle 577-617 and an intermittent miss you can feel.
TPS moves between 0% and 0.4% in a regular pattern. Not exactly a square wave, but close.
Intake manifold pressure is back and forth between 10.6 and 10.9 inHg. Similar to the TPS, but not exactly in synch, TPS fluctuates faster.

Am I looking at an injector problem - if so is it an occasional rich or occasional lean condition? The TPS is bumping to 0.4%.

anyone have a good idling unit they can put a scanner on and tell me if this is normal?

 

When I pulled the plenum I found signs of fuel washing on the drivers side of the engine in the intake runners. No sign of a fuel wash on any of the poppet lines or at the FP regulator. This is still the original style SCFI with poppet valves.

Key on engine off there is a fuel smell inside the plenum. In an earlier post I noted a fuel pressure leak-down concern.

I'm not sure why there is fuel in the runners and no sign of leakage on the spider assembly. Maybe poppets sticking open? Has anyone seen this before?

Looked a little more, thought a little more. I now think I have the poppets on the passenger side leaking fuel. Fuel is being sucked via vacuum through the runners.

 

I've replaced the spider assembly with the multi-port injection version and have seen an increase in average fuel economy. There is still a vibration at idle that feels like an intermittent miss. Maybe I am being too sensitive? I checked the specifications and at idle +/-25 and I appear to be within specification. I found:So I mapped advance v RPM v MAF and found that I was experiencing a (very) intermittent drop in ignition advance, especially at idle. I swapped the coil and ignition module with another vehicle and found that the intermittent drop in advance went away.

I am still bothered by my idle. After the ignition module and coil swap, at a warm idle:I still have the TPS reporting both 0% and 0.4% at idle - I don't know if this is within specification or not. I cannot figure out why tps would change when I am not touching the throttle.

Does anyone have any ideas?

 

xxxxx

 

Kevin,

We have a 99 Bravada 4.3L and a 98 S10 4.3L. The Bravada does not have an intermittent miss at idle. The S10 does. I have done a complete tune up to the S10 to include the following:
plugs
wires
distributor cap
rotor
new MAF
fuel pump
ignition switch
cleaning of manifold and exit points of fuel injectors during LIM gasket replacement

None of the above resolved the slight intermittenment miss at idle. I don't have the tools nor the experience to do all the testing you have done. My next steps are:
Replace fuel pressure regulator
Replace fuel filter
Replace EGR


Just wanted to share what I have done (that didn't work) and what I will be doing.

Good luck,

Mike

 

Update on the TPS readng that fluctuates at idle. Since I could find no mechanical reason for the fluctuation I looked for electrical. Suspecting a fault in the PCM ground path I was able to swap another handy PCM and the fluctuation is now gone. It was either the wiring harness connection at the PCM or the PCM.