high idle
Thread Starter
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Junior User
Joined: Jul 2007
Posts: 65
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high idle
ok, so my truck (96 f150 5.0 v8) hasnt been running its best.
maybe 2 months ago the check engine light came on so I took it in for testing.
I was told that there was a misfire on cylinder 7 so I replaced the plugs and wires. then about a month later, I replaced the distributor cap and rotor.
now, not long after I put the new plugs in it started idling fast (anywhere from 1100 rpm to 1700) but will usually will slow down after a few seconds, till I gas it again.
I took it to the shop yesterday and was told that I had the wrong type of plugs, but other then that, he said all looked good. so I went out and got some motorcraft plugs and new wires, and it changed nothing. then I was told on another forum that the IAC might be bad. so, replaced it this morning and theres no change at all.
I checked the compression on the misfiring cylinder and its all good. but really, Im not sure if its still misfiring at all.
I was also told that there might be a vacuum leak, but I dont know where to look, or how to spot one.
I need to know what to do next.
any help would be greatly appreciated
maybe 2 months ago the check engine light came on so I took it in for testing.
I was told that there was a misfire on cylinder 7 so I replaced the plugs and wires. then about a month later, I replaced the distributor cap and rotor.
now, not long after I put the new plugs in it started idling fast (anywhere from 1100 rpm to 1700) but will usually will slow down after a few seconds, till I gas it again.
I took it to the shop yesterday and was told that I had the wrong type of plugs, but other then that, he said all looked good. so I went out and got some motorcraft plugs and new wires, and it changed nothing. then I was told on another forum that the IAC might be bad. so, replaced it this morning and theres no change at all.
I checked the compression on the misfiring cylinder and its all good. but really, Im not sure if its still misfiring at all.
I was also told that there might be a vacuum leak, but I dont know where to look, or how to spot one.
I need to know what to do next.
any help would be greatly appreciated
Postmaster
Joined: Jul 2006
Posts: 3,978
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From: Central PA
welcome to FTE
There are guys on here that can tell you serial/parts numbers from memory . But Im not one of them .
You can use propane gas to check for vacuum leak . Just hold non light torch around all lines. As for miss my last truck the injector harness was going bad. Also the routing od wires is important on the 302 . Check for cross fire.
But you will get some real ideas and the way to check them out here. Its a really good sight.
LOST
There are guys on here that can tell you serial/parts numbers from memory . But Im not one of them .
You can use propane gas to check for vacuum leak . Just hold non light torch around all lines. As for miss my last truck the injector harness was going bad. Also the routing od wires is important on the 302 . Check for cross fire.
But you will get some real ideas and the way to check them out here. Its a really good sight.
LOST
Posting Guru
Joined: Mar 2007
Posts: 1,119
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What he meant about the propane was by letting some propane seep around the line, if there was a leak, it would get sucked into the engine and would cause the engine to rev up. Also, those wire stays for the plug wires are necessary so they dont crossfire or ground out.
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Junior User
Joined: Jul 2007
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Originally Posted by boggerted
What he meant about the propane was by letting some propane seep around the line, if there was a leak, it would get sucked into the engine and would cause the engine to rev up. Also, those wire stays for the plug wires are necessary so they dont crossfire or ground out.
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Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
Originally Posted by ducky17
ah, I see. another thing I need to know is, what lines with leaks would cause a high idle?
It could be any of the following:
Any vacuum line.
Brake booster diaphragm.
Intake gasket leaking.
Throttle plate not closing.
Vacuum reservoir canister rusted out on the bottom.
Last edited by subford; Jul 15, 2007 at 04:59 PM.
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Elder User
Joined: Sep 2005
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From: Orangeville, Ontario
I've got the same issue except mine goes a wee bit higher than 1,700 rpms sometimes. I'm replacing my TPS (throttle position sensor) tomorrow since I know it's bad. I'll let you know if it helps at all. I've also been told I need an IAC but that's not for sure so I'll wait til' I'm done the TPS to do that.
