'89 S10 4.3 erratic idle speed

[76C10Stepside]

My recently acquired 1989 S10 with 4.3 Vortec engine and A/C idles funny.
When first started up, it idles very fast for about 30 seconds or so, then slows down, but for the first minute or so of driving, the idle speed keeps stepping up and down. It also steps up and down constantly when idling, but drives just fine. It sounds like the A/C is engaging/disengaging when the idle speed changes. The graphical tachometer stays at the 750 mark with no visual indication that the idle is stepping up, maybe it's just because the resolution is so low (looks like 250 RPM increments, but will have to check next time I drive it).

I haven't tried reading the error codes from the ECM yet, no shop manual, but guessing it's like my '87 Buick, where you jump two pins on the panel after disconnecting/reconnecting the battery to reset codes and start the engine to register any new codes.

Thinking it's either a dirty or bad mass-airflow sensor or a problem with the A/C. Or is this "normal"?

[ProStreet68SB]

Unless you swapped a vortec in, it should just be a TBI 4.3 correct?

[76C10Stepside]

Originally Posted by ProStreet68SB

Unless you swapped a vortec in, it should just be a TBI 4.3 correct?

I was going off my Dad's notes that said 4.3 Vortec engine was a "must have", but the dealer invoice just says 4.3 TBI. Just took the air cleaner off and you're right, it does not have the Vortec intake manifold. :-(
What I read says the 4.3 Vortec was introduced in '85 and available on S10/S15 starting in 1988. Oh, well.

Do these have a mass-airflow sensor or MAP sensor? Where it is? The air cleaner and snorkel do not have any electronics in them. All my other cars have carbs, LOL.

I tried to transfer the title today and was told I have to get an emissions test first, dang it! It's one year too "new". The testing stations were already closed by then. I'd like to check for trouble codes and take care of anything needed if possible before I take it in for testing.

The under-dash connector has 12 pins. That's all's I know. Thanks!

[BlackedOut67shorty]

They were vortec heads on them so it is a vortec, just the begining year. If its pulling up codes is buy myself a Haynes book and get a paper clip and start checking codes. It will at least bring you into the ballpark with what's wrong instead of replacing things that shouldn't be replaced. It could possibly be tps, egr, map sensor, list is limitless on what it could be. Your s10 should know what it could be by using the pins below the dash
Posted via Badass Mobile Device

[76C10Stepside]

Originally Posted by BlackedOut67shorty

They were vortec heads on them so it is a vortec, just the begining year. If its pulling up codes is buy myself a Haynes book and get a paper clip and start checking codes. It will at least bring you into the ballpark with what's wrong instead of replacing things that shouldn't be replaced. It could possibly be tps, egr, map sensor, list is limitless on what it could be. Your s10 should know what it could be by using the pins below the dash
Posted via Badass Mobile Device

Oh, really? Great news, thanks!

Was hoping someone could tell me which two pins to jumper, and if any error codes stored, post them here and ask someone to look them up, LOL.
I found this list of ODBI codes for "4.3L VIN Z and W" - the 8th digit in my VIN is "Z", so I guess this is the right list for me:

http://www.s10forum.com/forum/f107/d...-codes-198381/

[76C10Stepside]

The 12-pin ALDL connector on my '89 S10 4.3 only has pins in A, B, C, E, F and H. Search for pictures found many different pinouts, did not see any that match mine.
Are the following pinout mappings correct for my truck? Note that D, I, J, K and L are missing from list, and there is an "M"!:

A - Ground
B - Test Terminal
C - Air Injection
E - Serial Data
F - TCC
G - Fuel Pump
H - Brake Sense Speed Input
M - Serial Data

[BlackedOut67shorty]

If you buy a Haynes book it will tell you which wires you need to touch . I can try and find my book and take a pic of how to search for trouble codes
Posted via Badass Mobile Device

[76C10Stepside]

OK, I only got code 12 "Diagnostic mode" (flash, pause, flash flash) three times in a row, no other codes. If any other trouble codes had been stored, there would have been other codes after the first or second time flashing the code 12, right?

Will look for a used Haynes manual. Anybody have the 1989 Light Duty Truck Unit Repair Manual published by helminc.com? Is this a valuable book to have for the shadetree S10 mechanic?

[76C10Stepside]

The S10 passed emissions on the first try, and no line at the testing station. This should be the LAST TIME EVER. Yea!

Sticker on windshield says I have another 1k miles before next oil change. I wonder how LONG it's been??? Still under 45k on the ODO. That's only 1,875 miles a year! Talk about "low mileage"...

Was surprised to find that the A/C works. When I went through all the old paperwork, found one stating that the A/C was not cold, but nothing to indicate it had been charged or converted per recommendation of the shop.

One invoice says the electronic instrument cluster was replaced in '92. Another invoice in '99 says cluster intermittently won't come on or goes off. Another invoice in '99 says they removed/replaced cluster and tested ok. There was another invoice claiming cluster had been sent out for repair, can't find it now.

30k mile service was in '99. Wow, 10 years to reach 30k! 45k mile service was in '03 at 41k miles.

The wipers often go one time around by themselves when I turn right and sometimes without doing anything. Guessing it's a wire has worn insulation at some critical point. Found an invoice from '96 mentioning this problem, says "need to replace switch", $125 parts/labor. Guess it never got done. Funny, I've had two other GMs with this same turn signal/wiper stalk (with delay and washer) and never had any problems.

Ignition module and pickup coil replaced in '98. Cap, rotor, wires replaced in '98.

Starter replaced in '96. Coolant temp sensor replace in '03 (says engine would not start?).

[BlackedOut67shorty]

Wow that's pretty crazy. But its nice to know that it has been well maintained. Still gotta get mine inspected since last month, gotta get it aligned and get some good rubber on. Hope ya get a lot if miles out of your 4.3
Posted via Mobile Device

[76C10Stepside]

Thanks, me too! That's one ominous looking '67 you have there!

[76C10Stepside]

Update:

I ended up rebuilding the TBI, then one of the injectors failed and leaked a ton of gas into the crankcase, and the Throttle Position Sensor died (from gas getting on it?). Replaced the bad injector and installed new gaskets again. It ran well for awhile, but the high idle on cold starts continued (some say this is "normal", but I don't see why).

Then 2 months ago, it started running really rough on the way to see my GF. After I parked and got back in to move the truck, it would not crank. It's been sitting since then. The ignition switch and neutral safety switch both tested good, and had power to the crank fuse. NO trouble codes in the ECM. Since it had a NEW starter from last summer, I did not just want to replace the starter. Towed it to a new shop I've been wanted to try out, and they said the started shorted out. Had them install a new starter (too damn cold out).

It's still running rough at idle and at low speeds, seems to smooth out around 35MPH, but have only driven it a few miles on the street so far. Also, the Temp Guage stopped working this summer too. SO...

Back to my original question! Does this truck have a Mass-Airflow Sensor OR a MAP sensor? Whichever one it has, if it's bad, shouldn't I get a trouble code? When the MAS went bad on my '87 Buick, it had the same symptoms and tripped two trouble codes, first code said bad MAS, replaced the MAS and that fixed it. TIA

[76C10Stepside]

Thinking I had a bad fuel pump, I started diagnosing today, but the engine surprised me and started right up. But it idles way too high (last time checked, 1700rpm).

Checked for trouble codes and found Code 21(Throttle position sensor/voltage high). There were no trouble codes when I was trying to diagnose the no-crank problem.

Note: I had to replace the TPS after rebuilding the TBI a year ago, because I left it on the throttle body when I cleaned it with spray carb cleaner, which I guess damaged the TPS.

Removed the (new) TPS and verified the spring is not broken and it snaps right back, so not a mechanical problem. Engine ran the same with the TPS disconnected (and when removed from the TBI)--too fast and kinda rough.

The TPS plug and 6 inches of wire back to the harness look good.
TESTED TPS:
1. Input Voltage (unplugged): 5.05 volts (steady), OK.
2. Resistance: 1.5-6.9 on the 200k scale, smooth progression and consist results every time. Is this the right range?

What should the resistance be a zero throttle? This is a Gen 1 (OBD1) 4.3 early Vortec truck with non-adjustable TPS (unless you count bending the tab). Throttle is fully closed and does not stick. ANYBODY?

[Cali72K20]

Check your distributor. Mine just failed while driving, no codes other that 12. I had to have it towed home thinking it was a fuel issue. The reluctor wheel, looks like a star on top, just came apart in chunks, it was all rusted out. I had just replaced the cap, rotor, wires and plugs only 8K miles ago and the distributor looked just fine. I replaced the IAC at the same time as the tune up, because of the idle-same exact problem you have now. Mine has 140K original miles. NAPA part number 48-1635. She fired right up first try and purrs like a kitten!!!!

[Cali72K20]

this is from another forum, scroll down for the pictures:

http://www.elcaminocentral.com/showthread.php?p=464783

I didn't take any pictures of mine, I just threw it in the trash because I was mad that was the problem. Not the core, just the broken pieces of the reluctor wheel. There is a $55.56 core for the distributor from NAPA.

I didn't check for a short in the wiring at the connector, mine was a rusty broken mess.

Casey

[76C10Stepside]

I ended up finding a way to test the output voltage by inserting a piece of thin wire. Even though the TPS passed the resistance test with flying colors, it failed the output voltage test. Bought a new one at Autozone, but the harness plug would not plug in all the way, and it did not work (looked like a cheap rebuild, had plastic shaft that probably would have broke eventually). They didn't have another one, so I got my money back and bought one at O'Reilly's, and that one works.

Next step is to figure out where the coolant temp sensor that sends to the temp guage is, guage stopped registering at all awhile back. There's one at the front of the intake manifold (somebody said that's the wrong one?).

Pretty sure my C10 has a spun bearing, so real happy to get the S10 back on the road.

[Alderfek]

Originally Posted by 76C10Stepside

Next step is to figure out where the coolant temp sensor that sends to the temp guage is, guage stopped registering at all awhile back. There's one at the front of the intake manifold (somebody said that's the wrong one?).

Coolant temp for the computer is in the manifold next to the thermostat housing. Gauge sensor should be on the side of the drivers side head.