89 d150 318 TBI Stalls & Idle raises and lowers after engine heats up

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Instigate

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Ram Year
1989
Engine
318 5.7L
1989 Dodge D150 318ci TBI 2wd 1/2 ton Automatic

Symptoms:
Idle raises and lowers, after warming up.
Engine stalls when you come to a stop, after the engine warms up.

Things I have done:
Checked for injector operation.
Replaced fuel filter.
Checked fuel pressure.
Replaced cap, rotor, plugs, and wires.
Tried blocking the EGR.

Checked for vacuum leaks.
Checked throttle body mounting bolts.
Checked throttle position sensor, MAP sensor, and CTS.
Checked throttle body temp sensor but am not sure of the results.
Checked the IAC but am not sure of the results. I numbers I got were not in spec. But I'm not sure if it's the sensor itself or maybe some other sensor or component that is messing up my results.
 

Deblackmon3

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Sep 7, 2013
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Location
South Carolina
Ram Year
1990
Engine
LA 318
1989 Dodge D150 318ci TBI 2wd 1/2 ton Automatic

Symptoms:
Idle raises and lowers, after warming up.
Engine stalls when you come to a stop, after the engine warms up.

Things I have done:
Checked for injector operation.
Replaced fuel filter.
Checked fuel pressure.
Replaced cap, rotor, plugs, and wires.
Tried blocking the EGR.

Checked for vacuum leaks.
Checked throttle body mounting bolts.
Checked throttle position sensor, MAP sensor, and CTS.
Checked throttle body temp sensor but am not sure of the results.
Checked the IAC but am not sure of the results. I numbers I got were not in spec. But I'm not sure if it's the sensor itself or maybe some other sensor or component that is messing up my results.

The throttle body temp sensor mainly makes sure that the fuel mixes correctly when the engine is hot. Since you mention that all of this happens after it's warmed up, I would test that sensor more. Get an OBD scanner and scan the computer. If you get 23, then it's a problem with the sensor and needs to be replaced.

If your sensor reads out 25 though, then it's the IAC.
 
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Instigate

Instigate

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Thank you for your post Deblackmon3. I ended up checking the fuel pressure regulator and gas poured out of the vacuum line! So I put a new fuel pressure regulator on and now it idles fine but only in drive and rev, in order to keep it running I have to start it then immediately throw it in drive. If I leave it in park or neutral it stalls immediately. So I'm thinking it has to have a vacuum leak or a busted diaphragm somewhere? I've replaced a ton of the vacuum lines to try to eliminate any vacuum leaks. Thank you for your help.
 

Deblackmon3

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1990
Engine
LA 318
Thank you for your post Deblackmon3. I ended up checking the fuel pressure regulator and gas poured out of the vacuum line! So I put a new fuel pressure regulator on and now it idles fine but only in drive and rev, in order to keep it running I have to start it then immediately throw it in drive. If I leave it in park or neutral it stalls immediately. So I'm thinking it has to have a vacuum leak or a busted diaphragm somewhere? I've replaced a ton of the vacuum lines to try to eliminate any vacuum leaks. Thank you for your help.

Diaphragms are found in the transmission, so that wouldn't be the issue causing it to stall in park/neutral. If you redid most of the vacuum tubes, recheck the connectors for them and make sure you tightened them enough but didn't over-tightened. I don't know your experience with cars, but my advice would be tightening the bolts by hand until you can't anymore, then use a box end wrench and give it one good tug.

Check the MAF sensor too, that'll be inside the air cleaner with some vacuum tubes coming from the throttle body and into the air flow flap. Sometimes they get gunked up by debris. Just clean it with some throttle body cleaner, give it a good soaking.

Finally, nothing beats a good ol' compression test.
 
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Instigate

Instigate

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Ram Year
1989
Engine
318 5.7L
I already tested the MAF. The diaphragms I was mentioning are ones like the one in my fuel pressure regulator, gas got into my vacuum system so the gas could have damaged other diaphragms right? I was thinking that a vacuum leak would cause it to stall in park or neutral because of the vacuum drop. But I did end up finding a broken hose, so I replaced that and reset the computer and now it will idle fine. But now what it's doing is stalling. I need to drive it a little more to pin point when exactly it's happening. But it seems like idk, I'm at a loss. I've tried so many things.. I'll do some more testing tomorrow and post again with a better description of the symptoms now.
 
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Instigate

Instigate

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Ok, so it will idle fine in all gears now. But when I drive off there is a lot of hesitation and the engine ends up stalling. I checked the flash codes and I got:
37 "Torque converter clutch solenoid circuit. An open or shorted condition detected in the torque converter part throttle unlock solenoid circuit (automatic transmission model only.)"

I tried to find some info on it in my haynes but there is no mention. I will do some searching online. I hope someone here knows what this is.
 
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Instigate

Instigate

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I missread what I wrote down when I recorded the flash codes. I didn't realize till I when back and looked at what I wrote again. It was 36, not 37. So that is solenoid coil circuit (air switching). And sure enough there was a short. So I fixed that up and ran out of daylight. So I'm going to take it for a test drive tomorrow and I'll post what happens.
 
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Instigate

Instigate

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I took it to a friend of a friend that's a mechanic and he looked it over and said that I prolly have a vacuum leak at the intake manifold gasket...

He did the, spray brake cleaner around the edges of the intake manifold and I thought I heard the idle speed up at one point but I'm not 100% sure and neither was he. I'm going to try to figure it out today. If not, then I guess I'll replace the gasket.

I used propane to check for a vacuum leak all around the intake manifold and around all the hoses. The idle didn't change. So I checked the resistance of the ignition coil and I got an infinite reading. So I'm about to head out and get a new one. And now I'm remembering last time I tried to buy a new coil for this truck I couldn't find it. The one that came off the truck says "No external resistor required" and I think I remember the new coils at the store needed a resistor, maybe I'm remembering wrong. I hope I'm wrong. But ya, I'm off to get a new coil!
 
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Instigate

Instigate

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1989
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So the new part gave me the same readings as the one off my truck. I was talking to the mechanic that works in the shop next to NAPA and he was telling me that an infinite reading between the pos and neg terminals doesn't necessarily denote a bad coil. Which I still don't fully understand. I don't know where to go from here...
 
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