I've been working on my 89 K5 Blazer with a 350 TBI and I've replaced the following parts:

New IAC, new TPS, new EGR valve and solenoid, new cap, rotor, wires and spark plugs, new O2 sensor, new knock sensor, new PCV valve, new pickup coil and inner distributor shaft, and a new MSD blaster late GM coil. I have an Edelbrock Performer TBI intake on it also. I have an ADS Super chip in it and I removed it and put the stock chip back in it and that didn't do anything. I did a fuel pump pressure test and it has 11.5 lbs at an idle and drops to 11 lbs under a heavy load. I did a vacuum check off of the manifold tee for the brake booster and it has 18.5 lbs at idle. I removed and cleaned the TBI when I changed the IAC and TPS. I have 3" exhaust from the y pipe back with no cat. I tested the ECT when the engine was warm by unplugging it and the rpms picked up about 200 rpm. I did a compression check and all the cylinders have 125# of compression.

When I start the rig in the morning it will idle a little rough like it has a miss, and the rpms will bounce up and down from 800 to 500 rpm for about 1/2 a minute. Then when I take off it has a slight hesitation when I give it some gas right off idle. It runs great down the highway and doesn't have any other driveability problems except for down at idle. Even after it's at operating temp and sitting at a stop light, the idle will bounce up and down about 100-150 rpm and idle rough(but not like a miss). I checked the throttle shaft on the TBI but I couldn't get any play out of it. It has thrown code 43 once or twice, but the SES light hasn't come on for about a week or so. Could it be the ESC module is going south on me? If so, how much $$ are we talking for one of those? Any help or direction would be greatly appreciated since I've already dumped $400 into all the tune up and emission parts this last month.

Thanks,
Doug

 

i am kind of having the same problem but when i changed the esc it didnt work, the only thing i havent changed is the pickup coil, and the ecm. so if you change the ecm let me know how it worked plz

 

mine is doing the same thing. i just replaced the egr valve to get it to pass emissions and it just did 161 rwhp on a chassis dyno, so i don't think there's anything wrong with plugs, wires, ignition, etc.

anyone have any ideas?

 

This evening I went into town and on the way back home, my check engine light came on and stayed on for a while, then it went off. Then it came back on a few miles down the road and stayed on for a while again before going out. I got home and checked the codes and they're 42 and 44. I'm beginning to think my ECM is going bad. Anyone have any ideas?

 

Except it smooths out and runs great when the engine hits operating temp.

I've got a 1996 Vortec 350 longblock in mine with an Edelbrock Performer Vortec intake and Holley TBI adapter plate. No vacuum leaks anywhere, but I only get a reading of 15" of vacuum measured at the EGR port on the throttle body.

Only got one response when I asked my questions. Hope you have better luck. I'll monitor this thread. I too have spent quite a bit on parts, installing all new sensors, plugs, wires, cap, rotor, ignition module, tried another ECM, etc......right now I am just living with it. Got 20mpg on the highway to Lubbock last week, so highway driving is not a problem.
The problem, for me, is coldstarts, like when I get off work in the mornings.

 

I have the same problem with my 90 Z71. I just installed a 97 Vortec long block as listed in my sig.
I currently have the timing at 8°.
It runs like it has a miss when idling in open loop. Once it goes into closed loop, it smooths out.
I drove around with a Snap On scanner hooked to it yesterday and noticed the following
TPS Voltage at idle is .56 and WOT is 3.88
IAC counts where in the 15-20 range at idle in Park, but would go over 50 in drive
blm's would start at 130 and climb up to 140 when idling at a light (telling me its lean)
WOT O2 voltages were in the 680 range which is extremely rich. I know my 87 Grand National likes then in the 750 range.
I like many of you have replaced sensors, plugs and wires, cap and rotor, etc. I am thinking that it needs more fuel pressure to bandaid it for now. But I think some prom tuning is needed to fix it correctly.

 

badxs,

If you're having the same problems as I was with idle and taking off from a stop. then take off your dist cap, unplug your ignition module leads to the coil, remove the module with a 5.5mm socket, then unplug the two wire harness from the pickup coil to the module. Then get two small pieces of wire and hook them up to a multimeter and set it for milliamps. You should have at the minimum of .08 mA or 1 mA would be ideal. Anything less then that and you pickup coil is going south.

Last night I started the Blazer in the dark with the air cleaner removed and noticed the new autolite 8.5mm spark plug wires were leaking some spark at the boots on the spark plugs. It looked like 6 out of the 8 plug wires were doing it. So today I bought some MSD Helicore spark plug wires already custom made to fit my Blazer and it seemed to cure my driveability problem-at least 99% of it. I'll keep you posted after I start it up after it sits all night.

Doug

 

that is not a good way to check a pick up coil. you should check it for a/c voltage , and it should go high when magnet is lined up, and go low when un aligned.. on a scope it looks like a line with steps across it

 

same here i'm in this boat anyone got a clue some people say knock sensor but before i throw 34 dollars at auto zone i need more replies and if anyone has advice or answer i need it.

 

Even though I checked my fuel pump pressure and it was 11# at idle and 10.5# under a heavy load, I replaced the fuel pump, strainer and fuel filter and it cured my driveability problem I was amazed that my lazy fuel pump lasted as long as it did and not leaving me stranded somewhere.

Later,
Doug