Engine surges and stalls at cold idle


Nez'sRanger

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On my 1989 2.9 Ranger, I lifted the engine and changed the oil pump and oil pan gasket. It ran beautifully before I did that, but when I lowered it back down and reassembled it, she wouldn't run right. I finally got the timing right, but it was a fiasco, since it didn't want to stay running until it got to operating temp.
Now, it surges real bad and stalls at cold idle, and I have to give it gas to keep it running; however, when it is warm and idling ok, it is burning very rich. I can smell it bad in the exhaust. Any ideas? I'm pretty stumped... I've checked and double checked. I even but all new ground cables on sanded the contact points. Thank you!
 


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rusty ol ranger

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You didnt dick up the O2 sensor wire when you lifted the engine did you?
 

Nez'sRanger

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Any other ideas? I'm really stumped! I just changed the map sensor (I tested it with my multimeter and it was giving lower numbers than specs allow, which I imagine partially contributed to the rich issue)... Still runs horrible.
Like I said before, it surges real bad on startup and during idle as it warms up, but when it's warm, it runs ok, just ridiculously rich. I think it's pulling of less than 8 mpg now, and I've consistently been getting 16.5 before this.
I appreciate any help! This is my daily driver, and I'm a contractor, so I need it to run well ASAP!
 

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Check.timing with the tfi connected and disconnected. Heat is a giveaway that you have a coolant temp sensor wiring issue or a tfi issue.

Hall effect sensor is another possibility
 

Nez'sRanger

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Check.timing with the tfi connected and disconnected. Heat is a giveaway that you have a coolant temp sensor wiring issue or a tfi issue.

Hall effect sensor is another possibility
I recently changed the hall effect sensor (pretty much did a full distributor rebuild).
I wondered about the tfi, but thought it only caused surging when hot, and I have the opposite.

Do you mean actually unplugging the tfi, or just the spout?

I'll double check the coolant sensor and it's wiring.

Thank you!
 

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Check timing with.spout plugged in and unplugged. Should run somewhere around 20-23 degrees advance at idle IIRC.

There's a possibility yours has hit a point where just jarring it around is causing it to freak out and die when warming up.
 

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@Nez'sRanger did you get this figured out? I'm trying to troubleshoot the same issue on one of my trucks.
 

Nez'sRanger

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No, not yet. I've double checked a few sensor wires, and changed my fuel pressure regulator (cause it was leaking), but I've yet to check the O2 sensor, the timing, and the tfi. I'll let y'all know when I figure it out. Now that gas is up to 4.05 a gal here in socal, I've got a little fire under my rear to get to the bottom of it quick... I'm getting 12.5 mpg now!
 

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Cool. Thanks. I'm going to try changing the coolant temp sensor on mine first. Seems well within the realm of possibility for you since you just pulled the engine... maybe it got bumped or something, they are fragile. I'm dealing with a lot of weird issues, some of which were caused by sitting in a field for 8 years and some may have been present before it got parked. Hard to say and frustrating.
 

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I had my truck apart today for a water pump replacement and threw in a different, used coolant temp sensor while I was in there. I think it helped. I will have to fire it up tomorrow when it's fully cooled off and see if it's still surging at cold idle but my initial impression was that it was a significant improvement.
 

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I put some miles on the truck this weekend. I've found that it dies after 2-3 seconds when first started cold but after that it stays running and the idle is relatively stable - it'll go up and down 100rpm or so slowly but not the wild 500rpm fluctuations like before. I also threw on a spare idle air control valve for fun and that did not make much difference. I'm going to put a new thermostat in sometime this week as well - seems to run cooler than it should and I'm thinking that if the thermostat is stuck open it would not allow the coolant temp sensor to reach operating temp thus it would run richer.
 

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Fwiw, I had the same issue and beat my head against it for weeks. Changed everything from IAC to distributer and coil, to egr valve and sensors. Everything. Ultimately I did a smoke test and found that the lip on the air box you connect the intake tube to had torn and created a huge vacuum leak. I basically sealed the tube to the box with silicone and it runs and idles perfect now. I also got a TFI relocation kit and moved the TFI to the side of the engine bay at the same time so could have been that but really I think it was the vacuum leak. It drove me insane trying to figure it out.
 

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That is interesting that it even matters that there's an air leak there since it's in front of the throttle body and there's no MAF sensor to pull air through. I could see that being a problem on a 2.3 powered truck since the IAC is in another location near the air box and not on the upper intake, but not on a 2.9... I'd think you could almost run it with no intake tube at all, throttle body open to the atmosphere and it'd be fine.
 
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MMB

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I removed the vacuum hose from the brake booster and ran smoke into the intake from there. It just poured out of the box. I read the upper part of the box is sealed so assumed that was the problem and sealed it. It's possible that wasn't the cause but it did fix it after throwing parts at it left and right didn't. Like I said, I did the TFI fix at the same time so it's plausible that's what corrected the idle.
 


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