High idle/ poor performance issues
Thread Starter
Intermediate
Joined: Oct 2022
Posts: 39
Likes: 4
From: Ohio
High idle/ poor performance issues
1984 CFI, during warm up when my car hits about 130 degrees it idles at 2000rpm and hunts +/-200rpm. Also when at operating temp 185 degrees it idles fine but I get a lean air fuel mixture code and depending on whether or not that code is on depends on how good to car runs (typically). Checked vacuum I'm at a steady 15 in. Mercury which I belive to be low if I'm correct. But I noticed that when I unplugged my IAC valves it got rid of the high idle issue during warm up. So basically just want second opinions on weather or not it's IAC's, vacuum or both. Or maybe something else?
Thread Starter
Intermediate
Joined: Oct 2022
Posts: 39
Likes: 4
From: Ohio
I'll make sure to do that then, I've heard the gaskets around the manifold are pretty prone to leaks especially around the egr valve
Melting Slicks
Joined: May 2002
Posts: 2,255
Likes: 412
From: Muskogee OK
Cruise-In VI Veteran
Carb cleaner is safer to spray, or WD-40, doesn't risk predetonation like ether, or burn as hot.
Pull your EGR valve off the intake before the leak test and clean the tip and stroke it up and down a few times to ensure it's free. Will run lean if it's jammed open from carbon deposits. Take a vacuum to the intake opening from the EGR and blast the exhaust side, the one the plunger goes down into, with air compressor air on max to dislodge any carbon possible, but sucking it up with vacuum to prevent it from entering intake side
Pull, record, and clear codes, then drive above 35mph to have the ECM reset the IAC by fully extending the plunger and resetting the "counts" to zero, will then adjust to a new setting to maintain idle speed. Unless of course you have vacuum leaks somewhere
All of this is in the FSM by the way
Pull your EGR valve off the intake before the leak test and clean the tip and stroke it up and down a few times to ensure it's free. Will run lean if it's jammed open from carbon deposits. Take a vacuum to the intake opening from the EGR and blast the exhaust side, the one the plunger goes down into, with air compressor air on max to dislodge any carbon possible, but sucking it up with vacuum to prevent it from entering intake side
Pull, record, and clear codes, then drive above 35mph to have the ECM reset the IAC by fully extending the plunger and resetting the "counts" to zero, will then adjust to a new setting to maintain idle speed. Unless of course you have vacuum leaks somewhere
All of this is in the FSM by the way
Last edited by flannel_man; Jul 30, 2023 at 04:45 AM.
Melting Slicks
Joined: Dec 2009
Posts: 2,229
Likes: 284
I'd bet on the engine coolant temp sensor being bad, the 84s had a troublesome sensor and connector. Best bet is to update it. Sometimes you can wiggle it when it's running and the idle will return to normal. It at the front of the intake pointing forward.
Thread Starter
Intermediate
Joined: Oct 2022
Posts: 39
Likes: 4
From: Ohio
Isn't their a temp sensor in the Manifold itself that controls the vac doors on the air cleaner, at least I've been told that's what it is. Would that be worth replacing to while I'm at it?
Thread Starter
Intermediate
Joined: Oct 2022
Posts: 39
Likes: 4
From: Ohio
Carb cleaner is safer to spray, or WD-40, doesn't risk predetonation like ether, or burn as hot.
Pull your EGR valve off the intake before the leak test and clean the tip and stroke it up and down a few times to ensure it's free. Will run lean if it's jammed open from carbon deposits. Take a vacuum to the intake opening from the EGR and blast the exhaust side, the one the plunger goes down into, with air compressor air on max to dislodge any carbon possible, but sucking it up with vacuum to prevent it from entering intake side
Pull, record, and clear codes, then drive above 35mph to have the ECM reset the IAC by fully extending the plunger and resetting the "counts" to zero, will then adjust to a new setting to maintain idle speed. Unless of course you have vacuum leaks somewhere
All of this is in the FSM by the way
Pull your EGR valve off the intake before the leak test and clean the tip and stroke it up and down a few times to ensure it's free. Will run lean if it's jammed open from carbon deposits. Take a vacuum to the intake opening from the EGR and blast the exhaust side, the one the plunger goes down into, with air compressor air on max to dislodge any carbon possible, but sucking it up with vacuum to prevent it from entering intake side
Pull, record, and clear codes, then drive above 35mph to have the ECM reset the IAC by fully extending the plunger and resetting the "counts" to zero, will then adjust to a new setting to maintain idle speed. Unless of course you have vacuum leaks somewhere
All of this is in the FSM by the way
Melting Slicks
Joined: May 2002
Posts: 2,255
Likes: 412
From: Muskogee OK
Cruise-In VI Veteran
Bulk vac line is about $1 a foot. Easier to replace it all vs hunting leaks. If it's the original lines it's probably somewhere between brittle and split or gooey, and replacement will be your best bet.
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Thread Starter
Intermediate
Joined: Oct 2022
Posts: 39
Likes: 4
From: Ohio
Yes, it's the 1/4" wide 1 1/2" long thing on the bottom lid of air cleaner assembly, vac lines go to the bottom of it and to the flappers. Some people just get rid of the setup to gain an always open passenger side and the driver's side being open before the metal is @ 130⁰
Bulk vac line is about $1 a foot. Easier to replace it all vs hunting leaks. If it's the original lines it's probably somewhere between brittle and split or gooey, and replacement will be your best bet.
Bulk vac line is about $1 a foot. Easier to replace it all vs hunting leaks. If it's the original lines it's probably somewhere between brittle and split or gooey, and replacement will be your best bet.
Melting Slicks
Joined: May 2002
Posts: 2,255
Likes: 412
From: Muskogee OK
Cruise-In VI Veteran
Be really careful with the FPR on the rear tower. That thing will explode dramatically towards your eyes when you take the last screw out. There is a little knock out cap in the bottom of it that prevents you from adjusting the fuel pressure. Knock it out and toss it.
Hopefully you have the fuel pressure gauge set-up for adjusting fuel pressure and the specialty tool required to adjust it. If not do not replace the FPR, you'll never guess the correct amount of threads to adjust it to, and replacing it is pretty much impossible without backing the adjustment rod off all the way to keep pressure off the diaphragm for reassembly.
Hopefully you have the fuel pressure gauge set-up for adjusting fuel pressure and the specialty tool required to adjust it. If not do not replace the FPR, you'll never guess the correct amount of threads to adjust it to, and replacing it is pretty much impossible without backing the adjustment rod off all the way to keep pressure off the diaphragm for reassembly.
Thread Starter
Intermediate
Joined: Oct 2022
Posts: 39
Likes: 4
From: Ohio
Be really careful with the FPR on the rear tower. That thing will explode dramatically towards your eyes when you take the last screw out. There is a little knock out cap in the bottom of it that prevents you from adjusting the fuel pressure. Knock it out and toss it.
Hopefully you have the fuel pressure gauge set-up for adjusting fuel pressure and the specialty tool required to adjust it. If not do not replace the FPR, you'll never guess the correct amount of threads to adjust it to, and replacing it is pretty much impossible without backing the adjustment rod off all the way to keep pressure off the diaphragm for reassembly.
Hopefully you have the fuel pressure gauge set-up for adjusting fuel pressure and the specialty tool required to adjust it. If not do not replace the FPR, you'll never guess the correct amount of threads to adjust it to, and replacing it is pretty much impossible without backing the adjustment rod off all the way to keep pressure off the diaphragm for reassembly.