'87 R10 suburban 350 V8 TBI stalls at lights - suggestions?

[skizzik]

Replaced the coolant temperature sensor today, no change. Still stalling.

Spent some time trying to reconnect the socket for the Check Engine light by trying to reach it from under the dash but couldn't seem to get the socket back in. I just gotta turn the socket and it'll lock into place with the contacts touching the contacts behind it, right? Tried to take the rest of the dash off to get behind the speedometer but reached a roadblock there too. Don't wanna take too much apart since this is my DD.

Smier, I think you're right. I was so hopeful about the coolant temp sensor, but since that didn't work I'm officially hesitant to keep blindly replacing parts.

[skizzik]

Status update -

I fixed the SES light and pulled codes 24 (vehicle speed sensor), 33 (MAP sensor), and 44 (lean exhaust). These codes must have been stored in the ECM for a long time because my battery hadn't been disconnected in a long time. I noticed the Throttle Position Sensor and the end of the throttle shaft that it sits against were gunked up so I cleaned the area and put in a new TPS and then disconnected the battery for a few minutes to clear all codes and then went for a drive. It didn't stall while I drove but now it's running really rough at lights and the idle sounds really high when I switch to neutral or park. Pulled codes when I got home and picked up error 33 again (MAP sensor).

Thoughts?

Replace the MAP sensor? Is it possible the previous owner tried fixing the stalling-at-lights problem by turning the idle up too high and now all I need to do is turn the idle down? I should point out that all I did for the new TPS was stick it on. I was just reading online that many Throttle Position Sensors require initial adjustment - should I have done that?

[Desert1957]

Before you replace the "Map Sensor" I would make sure the vacum line going to it is in good shape. If it has a hole, or is disconnected the sensor will think the engine is wide open throttle and will go FULL RICH, poor idle , black smoke and other problems.

Remember "TBI" GM engines DO have a re-learn feature , everytime the Computer or Battery is disconnected , may take a few miles to re-learn all parameters.

Desert

[nlped]

I had pretty much the same issue with my old '87. It threw the MAP sensor code too, and like Desert said, I checked the vacuum line first & sure enough it had a small melted spot in it. I replaced the line, cleaned the vacuum source nipple (I love saying nipple ) out with some cleaner spray, and poof...Good as new. Give it a try.

I don't know about the TPS on these trucks, but I do know that you need to adjust them on some imports, and my mustangs. I'm sure someone can chime in on this though.

Good Luck,

Ed

[Smier]

Yes, thoroughly go over all vacuum lines for leaks. Another common symptom on these TBI motors with a vacuum leak is an unusually high idle. Another good source for info on TBI setups is thirdgen.org, it's a site dedicated to 1982 to 1992 camaros, but they used the same TBI setups on our trucks and there are a lot of guys on there that know there stuff!!! A simple google search will give you info on how to diagnose the codes. Remember, just because you have a map code doesn't mean the map sensor is bad... It could be or something else might be causing it to act up. But it will point you in a direction. Be patient, keep posting up what you find and guys will try and help you out. Take your time and inspect connectors and clean up things as you go, I actually was fighting several problems on mine at the same time which made diagnosing difficult at times. I'd fix a problem, and it'd run better, but not 100%.

[skizzik]

Latest update:

I've thoroughly checked for vacuum leaks - by spraying throttle body cleaner on all vacuum hoses and at the base of the throttle body and visually inspecting everything - and can't find any leaks.

I'm getting flash codes for the TPS and MAP sensor, even after replacing the TPS. I then decided to concentrate on the MAP error and assume the TPS error will go away when the MAP error does.

I noticed that the output of the throttle body (the part where the vacuum hose connects out to the MAP sensor) was clogged with gunk. I sprayed throttle body cleaner into it and tried cleaning it with q-tips and one of the cottony q-tip ends got stuck in the throttle body.

Is that worth worrying about? Is there a better way to clean that area? Once I'm sure that area is clean, my next step is going to be replacing the MAP sensor.

[Jonboy]

You will have to adjust the TPS voltage if you have replaced the sensor. IIRC, it should be .45V at idle (no pressure on the throttle) and ~5V at Wide open throttle (WOT). With a voltmeter connected, there thould be a sweep in the voltage readings from closed to WOT.

Looking at your other post, you will probably want to put in a speedo cable and see what that does. Driving with no VSS could have smoked the torque converter clutch, as well as given a lot of other false readings as well.

[skizzik]

I figured out my problem. Turns out I've got 2 issues, MAP error and VSS error. I'll talk about the MAP error here and close the thread, because I've gotten the MAP error to go away, and concentrate on the VSS error on my other threat.

The previous owner of my suburban disconnected the charcoal canister, so the tube to where the canister used to be is just sitting there. I just noticed that somebody (it must've been a mechanic, because it wasn't me) plugged the end of that cable with a bolt. I guess they thought it would cause a vacuum problem to have it not plugged? Anyway, when I took the bolt out, the MAP error went away.

Anyone have any idea why?

[skizzik]

OK I finally got this figured out... I think the plastic speedometer driven gear is stripped and not turning, so the speedo cable doesn't turn, so the speedometer doesn't work, so the VSS constantly tells the engine that I'm not moving.

I think all I've got to do is replace the speedo driven gear. The dealership doesn't even carry it anymore (at least the one I need, with 38 teeth), but I think I can get one online.

Thanks for everyone's help, I wouldn't have known how to pull codes without your help.

[skizzik]

this thread can be closed.