Setting idle 96' 351
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Setting idle 96' 351
I've been searching around on all the forums and using all the keywords I can think of, but I still can't find the thread. I know there used to be one around about properly adjusting your idle screw on the 90s EFI trucks.
I want to know how to adjust it properly so that way I can test if my IAC is bad or it's just my idle.
From what I can remember it involves moving the screw to the proper place then removing the plug from the IAC... if it dies you do one thing... if it idles for a few then dies you do another thing (like clean the plug out on the IAC.)
I can remember and I'm completely lost so if anyone has a clue about it. Do tell!!
I want to know how to adjust it properly so that way I can test if my IAC is bad or it's just my idle.
From what I can remember it involves moving the screw to the proper place then removing the plug from the IAC... if it dies you do one thing... if it idles for a few then dies you do another thing (like clean the plug out on the IAC.)
I can remember and I'm completely lost so if anyone has a clue about it. Do tell!!
The Southernmost Mod
Joined: Dec 2004
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From: Caracas, Venezuela
The Iddle screw shouldn't be messed with in these trucks, you can try searching in this section using the keywords "iddle screw reset" or something of the like, or you can shoot a PM to Greystreak, who posted the proper procedure.
Fleet Owner
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From: Kentucky
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So today I took apart the tb and cleaned the tb and the IAC without getting the electrical units wet. When I put everything back together and started the truck it was running really smooth at about 900 rpm. Then when I got in the truck and touched the gas to see it if would idle back down after hitting around 2000 it didn't. It stayed and idled at 2000 in P/N but in R/D it was down to 900. So I put the truck back in P and went and pulled out the IAC connecter and it instantly dropped down to 900 rpm again. This would mean the IAC is bad correct?
Also I'm fairly sure I don't have a vacuum leak. (Someone suggested spraying brake clean over the vacuum lines to see if I had a leak, so I did and didn't notice anything.)
Also I'm fairly sure I don't have a vacuum leak. (Someone suggested spraying brake clean over the vacuum lines to see if I had a leak, so I did and didn't notice anything.)
Fleet Owner
Joined: Oct 2005
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From: Kentucky
So today I took apart the tb and cleaned the tb and the IAC without getting the electrical units wet. When I put everything back together and started the truck it was running really smooth at about 900 rpm. Then when I got in the truck and touched the gas to see it if would idle back down after hitting around 2000 it didn't. It stayed and idled at 2000 in P/N but in R/D it was down to 900. So I put the truck back in P and went and pulled out the IAC connecter and it instantly dropped down to 900 rpm again. This would mean the IAC is bad correct?
Also I'm fairly sure I don't have a vacuum leak. (Someone suggested spraying brake clean over the vacuum lines to see if I had a leak, so I did and didn't notice anything.)
Also I'm fairly sure I don't have a vacuum leak. (Someone suggested spraying brake clean over the vacuum lines to see if I had a leak, so I did and didn't notice anything.)
Time to check for codes to see if the computer has something to tell you. I suspect a faulty TPS sensor. The output signal may be non-linear/noisy. But I highly suggest a code check before tossing parts at the problem.
As far as the so-called spray test on the vacuum lines go, I find it to be very unreliable. I use a hand-held vacuum pump/gauge set to test each vacuum circuit. By pulling the IAC and having the idle drop down to the ~900 RPM range that is already telling you the high idle is not caused by a vacuum leak.
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So then if I'm reading it all correctly. I need to hook a volt meter up to the first plug I can find after the TPS and check the volts as I slowly open/close the throttle and compare with the numbers on the chart. Then if all is fine at said plug, move further down the line until I find an issue.
Lead Driver
Joined: Sep 2002
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From: Gateway to the West
So, you disconnected the IAC with the engine at full operating temperature and the engine running... and it didn't die within a few seconds?
Then you have a vacuum leak or the throttle plates are not fully closing in the bores... which is still technically a vacuum leak.
I suppose there could be one long-shot of an issue that won't produce any fault Codes however, it would make the engine run extremely rich and make hot restarts difficult (hot soak condition). That would be a bad ECT or ACT sensor. These two thermal sensors "tell" the computer when the engine or the air entering the engine is cold.
Personally, I would run a KOEO and KOER test and see what the computer "tells" you is ailing the poor thing before replacing too much in the way of electronics.
Then you have a vacuum leak or the throttle plates are not fully closing in the bores... which is still technically a vacuum leak.
I suppose there could be one long-shot of an issue that won't produce any fault Codes however, it would make the engine run extremely rich and make hot restarts difficult (hot soak condition). That would be a bad ECT or ACT sensor. These two thermal sensors "tell" the computer when the engine or the air entering the engine is cold.
Personally, I would run a KOEO and KOER test and see what the computer "tells" you is ailing the poor thing before replacing too much in the way of electronics.
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Well yesterday after I had everything all cleaned, I started the truck and let it run for ~10 minutes. It idled at around 900 rpm and the engine didn't get any hotter then between the N and O on NORMAL. When I went and throttled up the truck to around ~2500 to see if it would come back down it only got as low as ~1800 in P/N, but in R/D it was down to ~900.
I disconnected the IAC when it was in P and the rpm dropped down to ~900. I killed the motor, plugged the IAC back in and disconnected the battery for ~5 minutes. Hooked the battery back up, started the truck back up and with my foot on the brake I ran it through all the gears and it stayed down at ~900 which I was pleased with. I revved it up to around 2000 to see if it would go back down and the lowest it hit was ~1000-1100 in P/N which is what it was when I started this whole thing!
So I gave up for the day and went inside.
I disconnected the IAC when it was in P and the rpm dropped down to ~900. I killed the motor, plugged the IAC back in and disconnected the battery for ~5 minutes. Hooked the battery back up, started the truck back up and with my foot on the brake I ran it through all the gears and it stayed down at ~900 which I was pleased with. I revved it up to around 2000 to see if it would go back down and the lowest it hit was ~1000-1100 in P/N which is what it was when I started this whole thing!
So I gave up for the day and went inside.
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The Southernmost Mod
Joined: Dec 2004
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From: Caracas, Venezuela
1000-1100 is a good iddle speed, the ECM in these trucks is programed to keep the revs a little up if the warm-up procedure isn't completed (you didn't complete it since you began shifting gears). I would say your truck is operating properly again.
Fleet Owner
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From: Kentucky
So, you disconnected the IAC with the engine at full operating temperature and the engine running... and it didn't die within a few seconds?
Then you have a vacuum leak or the throttle plates are not fully closing in the bores... which is still technically a vacuum leak.
Then you have a vacuum leak or the throttle plates are not fully closing in the bores... which is still technically a vacuum leak.
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