Need help sorting out no idle on new 5.7 TBI engine

[Chevyguy]

Hey Chevyguy, thank you. I have a spare TPS, i will just replace and see what happens. Are you saying the backward battery incident damaged the Oxygen sensor, or that was a separate issue? My O2 sensor is the single wire, which i assume works by varying resistance, and I don't think that there is any current to it when the ignition is off. i actually never did hook up the battery backwards, when i was about to hook up the second cable it gave me a major spark that is as far as that went. My alternator survived as well.

Vince, sorry for the excessive ignorance, i cannot figure out what you mean by checking CTS voltage

Charlie, check the CST by removing the wire connector and probing the sensor terminals with a multimeter set on OHMS. At 210 degrees F. You should show 185 OHMS. If it's higher your sensor is bad. Download the Driveability and emissions manual that's been stickied in one of the forums, I forget which one. If your CST wire connector look's like it's seen better day's replace it too. Check your grounds at that front stud that's right by it also. I believe the ECM is grounded to it.

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[Bextreme04]

The coolant temp sensor(CTS) has much more authority on the fueling tables than it should on many OBDI vehicles(TBI falls in this category). If you have a bad CTS, it can be telling the computer that the engine is at a ridiculously cold temperature and will cause the computer to dump tons of fuel in to achieve the same effect as a choke on a carbureted car. I had this issue on an OBDI Honda and it is apparently a pretty common failure mode on these year range vehicles. OBDII has better checks on reasonable sensor ranges and also doesn't give the CTS as much authority over the fueling tables, so you don't usually run into this issue or you get a sensor fault code on LS or Vortec engines.

 

[Vbb199]

As I have gotten up in years (i am 67) i find it easier to accept my mistakes and even laugh at myself when i screw up. In fact ol' buddy, you seem to have some sway in this chat room, i propose the creation of a category up there with "Engine and Performance" and "Suspension" and we can call it "******* mistakes" for people like me to relate our screw-ups and how we fix them (hopefully!).
I think i am getting close to finding my solution. Yesterday i redid the IAC relearn procedure and now i can see the pintle has moved, allowing more air, so that is working. i can get the RPMs down to around 1,000 but at this point very uneven. injector spray looks very even (injectors are new) exhaust smells very rich, and the running is rough. although it does not sound like a uniform miss, i yanked a spark plug cable from the distributor and did not notice any difference. replaced that and pulled the next one, same thing, no difference. so the problem may be in the distributor.
on hooking up the battery backwards, i would think most circuits are protected by a switch (wipers have a switch, fuel pump has a relay, etc) so those should not be harmed if batt is hooked up backwards. But there obviously are some things that are "on" all the time. the fact that i got a major spark when i touched the terminal tells me current flowed (backwards) somewhere. So we will continue with the trial and error to find what got fried. I am ready to replace the module in the distributor with the old one, or maybe just replace the old distributor alltogether. But it has been raining all day here in Memphis and since i work in my driveway it will have to wait.
Y'all be well and happy Thanksgiving everyone

Shoot im nobody special, just a young guy (26) that knows a tiny piece of the pie!


If youre getting a stinky exhaust that might be your CTS

Tps should show a smooth transition in resistance values (i dont remember what they were)

Like i said before theres a proceedure you can do with your multimeter to check the CTS and IAC voltage and resistance values to verify their integrity.

Your ignition module can also be taken to a auto parts store to be verified..

Just a thought

 

[Chevyguy]

Shoot im nobody special, just a young guy (26) that knows a tiny piece of the pie!


If youre getting a stinky exhaust that might be your CTS

Tps should show a smooth transition in resistance values (i dont remember what they were)

Like i said before theres a proceedure you can do with your multimeter to check the CTS and IAC voltage and resistance values to verify their integrity.

Your ignition module can also be taken to a auto parts store to be verified..

Just a thought

Heat that ignition module up before you test it. They fail when they are warmed up. The module could be bad and still pass if tested cold.

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[53charlie]

UPDATE; First my appreciation to all you that contributed your knowledge here. I ran out of ideas and the engine was still running terrible, so i took it to a shop. They discovered the valves were too tight! When I received the long block, it had a big red tag that said "CAUTION; this engine is equipped with adjustable valve train. Check and adjust valve preload if necessary when engine is installed". I did, and i thought the valves were too tight so i loosened them a bit. Well, the important thing is that the engine is now running smooth as silk. I checked the timing, reset IAC again and adjusted idle. I was going to take it out for a spin but as soon as i put it in Drive the engine dies. same in reverse. i am going to check the P/N switch to make sure it is dialed correctly. Hopefully if it is a little warmer tomorrow i fix that. thank you again!

 

[Vbb199]

UPDATE; First my appreciation to all you that contributed your knowledge here. I ran out of ideas and the engine was still running terrible, so i took it to a shop. They discovered the valves were too tight! When I received the long block, it had a big red tag that said "CAUTION; this engine is equipped with adjustable valve train. Check and adjust valve preload if necessary when engine is installed". I did, and i thought the valves were too tight so i loosened them a bit. Well, the important thing is that the engine is now running smooth as silk. I checked the timing, reset IAC again and adjusted idle. I was going to take it out for a spin but as soon as i put it in Drive the engine dies. same in reverse. i am going to check the P/N switch to make sure it is dialed correctly. Hopefully if it is a little warmer tomorrow i fix that. thank you again!

Yay!

 

[Chevyguy]

UPDATE; First my appreciation to all you that contributed your knowledge here. I ran out of ideas and the engine was still running terrible, so i took it to a shop. They discovered the valves were too tight! When I received the long block, it had a big red tag that said "CAUTION; this engine is equipped with adjustable valve train. Check and adjust valve preload if necessary when engine is installed". I did, and i thought the valves were too tight so i loosened them a bit. Well, the important thing is that the engine is now running smooth as silk. I checked the timing, reset IAC again and adjusted idle. I was going to take it out for a spin but as soon as i put it in Drive the engine dies. same in reverse. i am going to check the P/N switch to make sure it is dialed correctly. Hopefully if it is a little warmer tomorrow i fix that. thank you again!

Check your TPS. Should show about 1/2 a volt when at idle. I replaced mine because it went from .68 to 1.28 as the accelerator pedal was pressed slowly with the motor off but the key was on. My truck runs great now. I was able to use a scan tool on mine but you can do it with a multimeter. Just unplug the TPS wire connector and probe the sensor while operating the throttle. The voltage should stay consistent without gap's all the way to full throttle.

Clayton

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[53charlie]

thank you Chevyguy, i have checked the TPS and the CTS, both are operating in the proper range.
Since GM does not want people messing with the idle speed, there are no official procedures in the manuals to do that. My question is, once you reset the IAC to fully closed position, disconnect it, turn the engine on, do you set that base idle with the trans in Park? or in Drive? i set it with the trans in Park, and it runs like a Swiss watch, as long as i leave it in Park (or Neutral), but it dies immediately when put in Drive or Reverse. it also died when i turned the AC on, which tells me it is not the P/N switch

 

[Chevyguy]

thank you Chevyguy, i have checked the TPS and the CTS, both are operating in the proper range.
Since GM does not want people messing with the idle speed, there are no official procedures in the manuals to do that. My question is, once you reset the IAC to fully closed position, disconnect it, turn the engine on, do you set that base idle with the trans in Park? or in Drive? i set it with the trans in Park, and it runs like a Swiss watch, as long as i leave it in Park (or Neutral), but it dies immediately when put in Drive or Reverse. it also died when i turned the AC on, which tells me it is not the P/N switch

Set it in drive to between 575-600 rpm's. Set your parking brake and block the wheels so the truck won't roll. Ground A-B terminals on the OBD-1 plug under your dash like you do to read codes. Turn key on but don't start for 30 seconds then turn off and unground the A-B terminals in the OBD-1 plug. Under the hood unplug the IAC wire plug connector. Doing this keeps the computer from adjusting IAC which is now in the parked position. Restart your engine and set your base idle in drive with it warmed up. In park your idle should be around 800 rpm. Turn off the engine and reconnect the IAC wire plug connector. Restart your engine, your idle should be within factory parameters. You may have to drive the truck so the computer can relearn what it needs to. Clear any codes that may have occurred due to unplugging the IAC.

Clayton

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[53charlie]

Ooooooh that should make a difference to set the base idle in Drive! thanks so much Clayton.
On a completely unrelated subject I notice you are in Eugene, many years ago i attended that "other" college 40-50 miles north of you, lived in Corvallis and spent a summer working in Astoria. I bought from a graduating student a '66 Mustang 2+2, 289 4 barrel no accessories and 4 speed for $700 (that was in 1975 ) and when i graduated in '77 i sold it for $800 and thought I was so smart! that thing would be worth a fortune today.

 

[Chevyguy]

Ooooooh that should make a difference to set the base idle in Drive! thanks so much Clayton.
On a completely unrelated subject I notice you are in Eugene, many years ago i attended that "other" college 40-50 miles north of you, lived in Corvallis and spent a summer working in Astoria. I bought from a graduating student a '66 Mustang 2+2, 289 4 barrel no accessories and 4 speed for $700 (that was in 1975 ) and when i graduated in '77 i sold it for $800 and thought I was so smart! that thing would be worth a fortune today.

Your welcome Charlie, glad I could help out. I miss my 67 Camaro, and my 73 K5 Blazer. They were just old cars that ate alot of gas back then. I never figured they would gain the value that they have. Happy Holidays Charlie.

Clayton

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[Chevyguy]

Ooooooh that should make a difference to set the base idle in Drive! thanks so much Clayton.
On a completely unrelated subject I notice you are in Eugene, many years ago i attended that "other" college 40-50 miles north of you, lived in Corvallis and spent a summer working in Astoria. I bought from a graduating student a '66 Mustang 2+2, 289 4 barrel no accessories and 4 speed for $700 (that was in 1975 ) and when i graduated in '77 i sold it for $800 and thought I was so smart! that thing would be worth a fortune today.

Your welcome Charlie, glad I could help out. I miss my 67 Camaro, and my 73 K5 Blazer. They were just old cars that ate alot of gas back then. I never figured they would gain the value that they have. Happy Holidays Charlie.

Clayton

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[53charlie]

i just realized i neglected to update my sob story here! i finally figured out what the idle problem was, the distributor!! i put a new one and the truck idles perfectly. I had the front and rear suspension rebuilt (too heavy a job for this old guy ) using dropped spindles in front, and the higher spring support and shackles in the back, and just had the rear axle rebuilt with 3.42 gears and positraction. Next in line is to raise the carrier bearing for the two-piece driveshaft, as it is now working at an ugly angle. After that i will check the angle at the last u-joint, as it seems to me the pinion angle changed a little with raising the supports for the springs, maybe have to put some wedges there to correct it.