Need Help: Bad Idle !!!!!
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Tuned
Joined: Feb 2003
Posts: 426
Likes: 4
Need Help: Bad Idle !!!!!
The bad idle on my '87 F250 (300, of course) is driving me to drinking (more than usual). The truck runs great at speed, good gas mileage, and all that. When I let off the gas, though, it begins to miss and continues doing so after idling down to an idle speed. It feels like it's running on about 4 cylinders instead of six, loping along, very rough. No black smoke or such while it's idling rough, and it revs up quickly when I hit the gas. Any hints anyone can give me of what to check will be appreciated. I've gone over the basics, but I'm ready to start again,
Thanks
Thanks
Elder User
Joined: Dec 2003
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From: Miami
I got the same exact problem with my motor!!! It start's in the morning with a slight shake to it, but when it get's to temp it idles so rough, like it's missing (it's not). My throttle bodie is cleaned, no check engine light, nothing. 20,000 miles on re-build. The only conclusion I can come up with is the cat is plugged up, causing a high back pressure at idle, worse when warmed up!! Give it a little throttle and she purr's like a kitten. ****'es me off!!
Al
Al
Elder User
Joined: Dec 2003
Posts: 655
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From: Miami
I put a brand new throttle bodie gasket (felpro) on saturday the 20th, did not fix it!!! I cleaned the bodie while it was off, spotless. I.A.C. works , idle is where it is suppose to be, but she run's like crap at idle!! If you bring up the throttle a little bit smooooooth! Motor mounts are fine, I have 4 diffrent books, I have tried everything! The answer is going to come from an old trick a mechanic knows!! Something simple and cheap, I hope. I am trying to sell it and I would like to fix it before I do.
Thanks
Al
Sorry I stole your post Meck1, but we are after the same thing!
Thanks
Al
Sorry I stole your post Meck1, but we are after the same thing!
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Tuned
Joined: Feb 2003
Posts: 426
Likes: 4
No problem, Al, and I think you're right. Sounds like we've got the same problem. I put a vacuum gauge on mine, and it didn't show any sign of a cat blockage. Is there any other way to test this other than taking the cat off?
I will check the TB gasket this afternoon. I had already torqued the TB to make sure it was tight, but I didn't take it off to check the gasket.
My IAC valve is clean with good o-ring, gasket, etc. The Haynes Manual, though, says I should be getting 10.5 volts on the IAC solenoid when I'm actually reading full battery voltage. Does anyone know if this is or could be a problem.
Thanks for the suggestions so far. Keep making them, and I'll keep checking. Al is right. Somebody out there has the key to this gremlin.
I will check the TB gasket this afternoon. I had already torqued the TB to make sure it was tight, but I didn't take it off to check the gasket.
My IAC valve is clean with good o-ring, gasket, etc. The Haynes Manual, though, says I should be getting 10.5 volts on the IAC solenoid when I'm actually reading full battery voltage. Does anyone know if this is or could be a problem.
Thanks for the suggestions so far. Keep making them, and I'll keep checking. Al is right. Somebody out there has the key to this gremlin.
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Elder User
Joined: Apr 2001
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From: Glen Burnie Maryland
I WAS gonna say something about AMC.....but some of you guys are too young to remember.........................
try spraying some WD-40 around the upper intake manifold gasket area. This gasket is like 3 mil thick. I've seen spray paint lay down a thicker coat.
Larry
try spraying some WD-40 around the upper intake manifold gasket area. This gasket is like 3 mil thick. I've seen spray paint lay down a thicker coat.
Larry
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Elder User
Joined: Dec 2003
Posts: 655
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From: Miami
I did the WD-40 all around, also did the propane soldering torch. where you open the gas valve (DO NOT LIGHT IT) and with the long tip place it all along the intake manifold and you get the same results as you would with the WD, just get in alittle tighter! Meck1 check the back of your throttle plates, if you got build up on them, called coking, it will give you this problem. I put new plug's gapped correctly, cap and rotor, did the check for light show at night in engine compartment, but I will do that one again! Keep the suggestion's coming, I'll try anything!! You tell me to go outside and drop my pant's and fart 3 times to the west, I"LL DO IT, if it fixes my problem!!!
Al
Al
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Joined: Sep 2003
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My 95 misses at low idle right when it shifts 2nd 3rd and od once rms pick up some its ok only when rpms are slow have already done plugs wires cap rotor tp sensor and fuel filter also when i stop and put it in reverse engine wants to die
Elder User
Joined: Dec 2003
Posts: 655
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From: Miami
When you say leaking E.G.R. do you mean not closing all the way or a vaccum leak?
I noticed something today, you guy's tell me what ya think. I walked to the back of the truck and I could here popping. When I got down near the tail pipe the exhaust would make a popping sound. Sometimes constant and sometimes intermittent. I check under the hood the other night and no arching anywhere!
Al
I noticed something today, you guy's tell me what ya think. I walked to the back of the truck and I could here popping. When I got down near the tail pipe the exhaust would make a popping sound. Sometimes constant and sometimes intermittent. I check under the hood the other night and no arching anywhere!
Al
Senior User
Joined: Jul 2003
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It sounds like our trucks have the same problem, Al, my exhaust sounds the same way, and it's got a nasty studder to it through all the gears. My concern is that I just replaced the head gasket this past weekend and I hope that nothing's wrong internally i.e. the head.... I'm going to check for a air leak tonight...so any other suggestions on how to fix this problem would be welcome.
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