87 idle surging/stalling issues

[tc197]

Hey guys, I've been having some troubles with my 87 GMC V2500 where it idles weird at different points of driving. It always starts after a few cranks and usually it idles high for a few seconds before it levels off to a normal idle (seems normal). Half the time at this point it begins dropping in idle and surging back up while the other half the time it just idles fine. Regardless, if I give it a few seconds and a little gas to increase the rpms it smooths out and off I go. While driving, everything is great. Occasionally when I first start the truck from cold it lugs when I try to accelerate, but that also disappears a few minutes into driving. As long as I'm moving everything is smooth but when I come to a stop for longer than about 5 seconds the idle begins dropping and surging and I can see my voltmeter dropping to below 10 and back to above 12. If it does this surging 3 times or so the truck tends to stall, but it always starts back up right away. The only other thing I've noticed is that when I try to maneuver at low speeds like in a driveway where there's pressure on the power steering, the idle wants to drop and I need to keep my rpms up with gas pedal. I can almost make the truck stall by sitting there and turning the wheel hard one way without moving.

I'm not sure if these issues are connected but figured I'd try to give a complete story. Basically I'm looking for some pointers as to what direction I should be heading in terms of checking and testing. When the idle starts surging I see the voltmeter surging but I'm not sure which one causes which. Could it be fuel based, electrical based, or some combination of the two? Based on the fact that the truck always starts, it makes me want to eliminate the battery. My first guess would be the alternator but before I start tossing parts around I figured I'd look for some advice. Thanks in advance!

[Irish_Alley]

here you go. ive made a list of the tbi sensors and what they can do if theyre bad. right now its only a guessing game unless you can test the part and verify the issue. if you do find it please report back
http://forum.73-87chevytrucks.com/smforum/index.php?topic=29996.0

[tc197]

Thank you for that, I'll post my test results soon. Only question I have right now is if the CTS Is saying to take it out and then test it? Just wanted to make sure I understood that correctly.

[Irish_Alley]

you can but it doesnt have to be that way. you can just start cold and read it then as it warms up keep tracking it

[tc197]

Sorry it took me so long to get back with some results. We got slammed with snow and bad weather. Here's what I came up with:

CTS:
Cold reading: 4740 ohms
Reading after squeezing in hand for 20 seconds: 3540
Saw it creeping back up from 3540 when exposed to cold air again, seems functional to me.

IAC:
A to B: 47.1 ohms
C to D: 47.5 ohms
A to D and B to C: Infinite
Seems to be in range

MAP:
A to C: 5.00 Volts
A to B: 4.69 Volts
A to Ground: .4 ohms
A to B is slightly lower than the test procedure stated, but it was more concerned with A to B being the same as A to C so I'm inclined to say this is ok for now.

TPS:

Arm at Rest:
A to B: 1600 ohms
A to C: 5020 ohms
C to B: 5530 ohms

Arm Max Rotation:
C to B: 1480
A to B: 5660

The test indicated a circular connector whereas mine was flat, and the values seem to be significantly off so this may be on it's way out.

I was a bit confused on the o2 and knock sensor tests so I didn't get those done yet. I'm not quite following how to make those measurements/ where the knock sensor is.

[VileZambonie]

Check for vacuum leaks and or a blown TBI base gasket. Spray some carb clean at the base of the TBI with it running and see if changes engine speed.

[tc197]

Finally was able to find some carb cleaner and test for leaks. Spraying carb cleaner seemed to have no effect on the engine speed. It was considerably warmer tonight when I did the test, probably about 65 out, and the truck seems to run much better in the warmer weather. It started immediately and idled fine immediately. I left the air filter on and sprayed the cleaner at the base of the tbi system all the way around. I never heard the rpms change at all.