87 Silverado 350 tbi idling rough

[1fishinrogers]

I got another code coming home from work last night, 32 .  barometric pressure / map sensor circuit failure ? I did notice that the truck ran really good going to work ( 45 min. drive ) for about 30 min but I could tell something changed slightly, I had to push further on throttle to get to down shift for incline but didn't get cel. Coming home it ran slightly better until half way then got the light and weaker, not missing or anything just not near as responsive. I don't know if its something getting hot and breaking down or just coincidence ?

[VileZambonie]

32 is EGR - Are you sure you got the right code? If it's MAP check the vacuum supply and do a pinpoint test at the sensor.

[1fishinrogers]

I see what you are talking about, my book says Barometric pres sensor or egr diagnostic switch, but it is a 32 code. What do you recommend.

[VileZambonie]

Is the EGR system  hooked up?

[1fishinrogers]

no

[Tazman]

Would Noalox or penetrox work on the connections at the TPS or what would?The reason I ask is I have tested or replaced a lot of emissions items to solve a idle issue that I had.Now it is back to a degree my truck can run great one minute and have a surging idle the next.Also on an 87 with the TBI what should the idle be at when in park at normal temp?Thanks

[1fishinrogers]

The loping is most likely from a vacuum leak. If you check all the hoses and can't find anything check the intake manifold gasket and throttle body gasket. Thats what I'm doing now. The Nolox is probably not a recommendation by mechanics but I've used it for a good while and it does fine on automotive connections. I can't find the specs on the idle speed but it's probably between 750 and 850 rpms.

[1fishinrogers]

just checked the codes again and now have a 33 map sensor ?

[Tazman]

If I had a vacuum leak would it not be doing it all the time not just once in awhile?Thanks

[1fishinrogers]

have you checked for codes and make sure the egr valve is working accordingly with acceleration it could have carbon or be sticking open at idle, also check the vent on the egr vacuum control solenoid, it has to be open to allow the egr valve to function quick enough to prevent vacuum drop.

[VileZambonie]

What's the manifold vacuum drop to when it's acting up? If you have a meter and a vacuum pump (optional) you can easily test the map sensor.

[1fishinrogers]

Update, I just got back to working on my truck and have noticed that after clearing the same code over and over( 22 ) that a couple of things happen consistently, the engine runs fine, idles fine and changes gears up and down shifts perfectly for about 15 minutes then the same symptoms begin, code 22 starts down shifting from over drive to 3rd and back about 3 or 4 times then it doesn't want to down shift unless you press half way down and the idle speed increases to about 1000 rpm's it also idles very rich before and after. I am going to check manifold vac. asap and check signal voltage wire on tps back to the ecm for a break or bad connector but can anyone tell me if this is common to the ecm going bad or where else should I look.

[VileZambonie]

Test the tps by backprobing it with a T-pin. Set your meter to the dc volts scale, key on engine off, backprobe cavity C of the TPS (grey wire) you should have approx 5 volts. Backprobe cavity B dark blue wire and with the throttle closed you should see approx .5V - now slowly open the throttle and the voltage should steadily increase with no glitches all the way to approx 4.5V If there are any glitches replace the TPS. 

[1fishinrogers]

Thanks for all your help. I followed these instructions and got all correct readings but I was pretty sure that the problem was in this circuit. I took it one step further after following the other trouble shooting info you sent on checking the ecm and 419 circuit. I probed the signal voltage wire just before it goes into the ecm with the switch on and only had .01 volts, but I knew I had .62 coming through the tps so after closely checking the connector found that even though it look good, it had little to no connectivety with the tps. I have a new connector ordered and will follow up after install. Thanks again for all the info.