aggravating stumble
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aggravating stumble
Mine is an '87 F-250, 300. It runs great, idles well, with one exception. After sitting at idle (750 rpm) for awhile, like at a long light, it will suddenly drop to around 300 rpm, the stock oil pressure guage drops to 0, and the engine light comes on. It doesn't die, but just putts and stumbles and won't recover on its own. If I hit the gas, it responds immediately with no hesitation, oil pressure jumps back up, and the engine light goes off. A mechanical gauge that I added says the oil pressure is okay. This is not an earth shaking problem, but it is aggravating me. Does anyone have a clue what might be going on here?
This is a truck I've been working on for the last year, so the following on it are either new or nearly so: ignition module, TPS, MAP, plug wires, plugs, coil. I'll appreciate any hints you might have about this.
Thanks,
Meck
This is a truck I've been working on for the last year, so the following on it are either new or nearly so: ignition module, TPS, MAP, plug wires, plugs, coil. I'll appreciate any hints you might have about this.
Thanks,
Meck
More Turbo
Joined: Jun 2001
Posts: 572
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aggravating stumble
try cleaning your air bypass valve ( or idle air control). it sits on top of you trottle body. it is a cylinder with an electricle wire running from it. just unbolt it and clean inside it real good. this solved my idle problems
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aggravating stumble
Okay,
I cleaned the air bypass valve like you suggested. Two weeks of running seemed okay, then yesterday sitting at the bank drivethru window a long time idling suddenly it did it again. Idle speed dropped suddenly to around 300, stumbled along without dying, until I kicked it up with accelerator.
Do you have anymore suggestions as to what to try?
Again, this isn't an earthshaking problem, just aggravating, but these kind of "gremlins" drive me crazy 'til I can figure them out.
I appreciate your help--
Meck
>try cleaning your air bypass valve ( or idle air control).
>it sits on top of you trottle body. it is a cylinder with
>an electricle wire running from it. just unbolt it and
>clean inside it real good. this solved my idle problems
I cleaned the air bypass valve like you suggested. Two weeks of running seemed okay, then yesterday sitting at the bank drivethru window a long time idling suddenly it did it again. Idle speed dropped suddenly to around 300, stumbled along without dying, until I kicked it up with accelerator.
Do you have anymore suggestions as to what to try?
Again, this isn't an earthshaking problem, just aggravating, but these kind of "gremlins" drive me crazy 'til I can figure them out.
I appreciate your help--
Meck
>try cleaning your air bypass valve ( or idle air control).
>it sits on top of you trottle body. it is a cylinder with
>an electricle wire running from it. just unbolt it and
>clean inside it real good. this solved my idle problems
More Turbo
Joined: Jun 2001
Posts: 572
Likes: 1
aggravating stumble
>My old car did something ike that. All I had to do for that
>was fix the timing chain. Maybe that could be it. I don't
>know. That is the best I can do for ya.
theese 300's don't have timing chains. it is just strait cam gear to crank gear. no play there.(unless it ie extreemely worn out)
buddy the problem you are describing sound like air bypass valve to me. I had the exact same problem with mine and that was the problem.
there is a possibility that the electrical solenoid on the bypass vale is malfunctioning. you can test this sensor very easily with a standard voltage meter.
I don't have my shop manual with me, otherwise I would tell you how to perform this test and what the reading should be.
hopefully someone can fill you in on this. if not I will have my manual back this weekend. I can post the procedures then if you would like.
>was fix the timing chain. Maybe that could be it. I don't
>know. That is the best I can do for ya.
theese 300's don't have timing chains. it is just strait cam gear to crank gear. no play there.(unless it ie extreemely worn out)
buddy the problem you are describing sound like air bypass valve to me. I had the exact same problem with mine and that was the problem.
there is a possibility that the electrical solenoid on the bypass vale is malfunctioning. you can test this sensor very easily with a standard voltage meter.
I don't have my shop manual with me, otherwise I would tell you how to perform this test and what the reading should be.
hopefully someone can fill you in on this. if not I will have my manual back this weekend. I can post the procedures then if you would like.
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aggravating stumble
I'll check the solenoid on the air bypass valve. I've got the procedures somewhere, so don't go to the trouble of posting them.
I appreciate the tip and will post the results.
Meck
I appreciate the tip and will post the results.
Meck
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From: Flagstaff USA
aggravating stumble
Okay, interestingly enough, I have a 63, with the 223. I just had the exact same problem. Mine would idle and run okay, but unexplainedly drop to 400 rpm and not die, but just sit there. This was whenever it felt like it. Thought it was electrical, but when I put on the new carb I left out the needle and seat because I didn't know what it's purpose was and didn't have the right fittings to connect it at the time. So the fuel pump couldn't keep up with the big gaping hole going into the bowl, as I was informed by some people here.
What drew me to thinking it a fuel starvation problem was the clear filter had almost no fuel in it when it dropped to 400 rpm, and it sounds like what you're experiencing is a fuel starvation problem as well. Since I put the needle and seat back in, the problem went away and so far hasn't resurfaced.
What drew me to thinking it a fuel starvation problem was the clear filter had almost no fuel in it when it dropped to 400 rpm, and it sounds like what you're experiencing is a fuel starvation problem as well. Since I put the needle and seat back in, the problem went away and so far hasn't resurfaced.
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aggravating stumble
Okay, here is the next bit of the bad idle mystery. I cleaned the bypass valve (a couple of times), checked the solenoid and juice to the solenoid. There seemed to be no problem there, but the idle was still not right. I then disconnected the electrical connector and the truck idled the same. At that point, I took myself to Autozone and bought another air bypass valve. Put it on yesterday afternoon. Today, after about 50 miles of running, the idle is nice and even, never been smoother, but it is idling at about 1050-1100 rpms. Does anyone have any clue about what is going on here? Is there a "learning curve" on the computer after changing one of these? As far as I know there is no manual idle rpm adjustment on these trucks. Is my thinking right there?
One more time, I appreciate any expert opinions you can throw my way.
Thanks,
Meck
One more time, I appreciate any expert opinions you can throw my way.
Thanks,
Meck
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