IAC Issues

Deckenrod88 · #1 09-28-2019, 07:07 PM

I had a code that said I was having IAC issues. Bought a new one and installed it, and the check engine light is persisting. Advance Auto code reader reports same problem, and now my 99 4.0XLT will idle at 700-800 rpm, shoot up to 1500 rpm for a bit then jump back down. Does anyone have any ideas?

jw5333 · #2 09-28-2019, 07:45 PM

Remove it from the engine and use some carb/intake cleaner to carefully wash out the crude in and around the vavle . Parts store should have a new gasket for couple $$ when you put it back on. Should hopefully help. Also try unplugging the wiring while the engine is running , that should help prove the IAC vavle is trying to work. The engine should run different.. or low idle/stall/die. If all else fells, a new one is around $40.00 - $60.00 depending on where you buy parts.
Also check wiring connection , I believe parts store sales new replacement pig tail.

One last idea , wondering if it would help to unhook the battery for 15 min or so to help the computor recognize the replacement part you put on. I know after replacing the TPS its necessary to do this in order for the computor to read the correct potential of the new part. Or maybe the throttle position sensor " TPS "is given you trouble. Good luck.

Deckenrod88 · #3 09-29-2019, 11:51 AM

Before I bought the new one, I did pull the connection and that didn't change the idle at all, so I knew it needed to be replaced. The one I got at AutoZone was a $49 direct replacement with a lifetime warranty. It came with the gasket and I installed it in about 5 minutes. It is a higher, more consistent idle, but still fluctuates from 800-1500 rpms. Also, the idle still isn't changing when the IAC is disconnected, but it doesn't do the high idle jump. I'm going to try the battery disconnect trick, but am pretty limited as far as knowing what to do or how to do it. Other than the Haynes manual I bought, I have no knowledge of the vehicle or the previous owners, and am mechanically speaking, extremely limited in knowledge of this vehicle. I have any tool or lift I could ever need because of my career as a welder, but that's about it. Any and all recommendations are extremely appreciated

turismolover22 · #4 10-03-2019, 06:24 PM

Quote:

Originally Posted by Deckenrod88

Before I bought the new one, I did pull the connection and that didn't change the idle at all, so I knew it needed to be replaced. The one I got at AutoZone was a $49 direct replacement with a lifetime warranty. It came with the gasket and I installed it in about 5 minutes. It is a higher, more consistent idle, but still fluctuates from 800-1500 rpms. Also, the idle still isn't changing when the IAC is disconnected, but it doesn't do the high idle jump. I'm going to try the battery disconnect trick, but am pretty limited as far as knowing what to do or how to do it. Other than the Haynes manual I bought, I have no knowledge of the vehicle or the previous owners, and am mechanically speaking, extremely limited in knowledge of this vehicle. I have any tool or lift I could ever need because of my career as a welder, but that's about it. Any and all recommendations are extremely appreciated

Usually you need to disconnect the battery and key on the truck for 10 mins to clear ALL memory from the ECU. This allows the vehicle to start from square one, when re-learning idle strategies.