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Idle air control valve?

58K views 32 replies 8 participants last post by  MikeyinaYJ 
#1 ·
Okay so jeep drove just fine and dandy today to and from work. When I got home it say for 15 minutes then I left again drove maybe 10 miles came back home. Jeep say for a couple hours went out to start it to leave and it cranks and acts like it'll fire but didn't. I give it a little throttle and it fires up. Idles about 100-200rpms real rough. I can give it throttle it reacts as it should and after a couple minutes of idling rough it'll come up to the 600-800rpm range. During any of this I can drive the jeep no problems. If I shut it off and turn it right back on cycle starts over again. Idle air control valve maybe? 2.5liter 5 speed.
 
#4 ·
X2. I would also pull the throttle body, remove the IAC, and clean the housing so it looks new. It is possible something bypassed your air filter and is sitting where your plunger sits that controls the airflow when the throttle is closed.
 
#6 ·
If it is your TPS your check engine light should be on. No real way to check it I know of, just replace for $20. And dont clean your IAC. If you mess with it other than removing it your will cause more problems.
 
#8 ·
I doubt it is your TPS anyways. Normally your ride is jumpy and jerky with a bad TPS since it is detecting when you are hitting the gas. Since the air to the engine should never be below the amount required to idle I would say buy an IAC if you were going to spend money. That I know is about $35-$40. If you clean it and put it together and it makes no difference, you could remove the IAC and screw in the plunger about 1/4 turn. It may fix your idle, but is not where you would want to start. Then only way you should mess with the IAC itself is if you are prepared to buy a new one.
 
#10 ·
Like I said, not moving your TPS isnt going to cause problems. Your IAC will though since that is what controls the air bypassing the throttle.
 
#11 ·
Your tossed tells your oscar what to do and it can be checked with a multimeter....check for 12 bsc going to it and check for continuity if the sensor as you open the throttle ...a bad gps will cause low or rough idol and possibly cause it to not run without holding the gas....Haynes repair manual explains exactly how to check it
 
#13 ·
I have had both a bad TPS, and IAC go out seperately. The difference I found was that the TPS caused crap when I was moving like jerky acceleration and it sounding like it might die. The IAC caused problems no matter what. I had the opposite problem though, severely high idle since it was too open. I could see a TPS causeing problems with an idle though, since if the IAC thinks the throttle is open it might not let as much air through as it should. To be honest, those two pieces on the Throttle Body are a major pain in the ass if it doesnt give you the code to let you know which one is causing the problems.
 
#14 ·
When you key on, (not just crank), the IAC is supposed to retract back to let the air bypass the butterfly valve in the TB. My IAC would not do this sometimes, and sometimes it would be fine. If the IAC piston does not retract, no air will get through the TB, -unless you bypass the IAC and step on the gas pedal- (which lets in air through the TB via the butterfly valve), which is what you said you had to do to get is started.

Once the engine fires up, the TPS will relay it's position back to the ECC, and any degrees above 0 the IAC will begin to close, (at settings/degrees above idle rpm). If you take off the IAC, but keep the electrical connector on, you can key on and see the piston retract, (2 guys needed bc it happens fast). Do this several times and confirm the the IAC piston is actually moving like its supposed to be. An intermittent or slow to move IAC piston retraction/extension with give you the problems you've described.

A TPS's job at engine start is to tell the computer "I'm at 0 degrees". If you have a faulty TPS, the idle will be higher after start bc the computer will think it needs to send more fuel. A faulty TPS will also prevent the engine from spooling up/down like it should. Like I said before, the TPS doesn't really come into play until after the Jeep is started, then it becomes important.
 
#15 ·
It also smells to be running pretty rich. Idk if that is another indicator to me. I have driven the jeep around the block, came home shut it off immediately restarted it and cycle started again. Rough idle and not wanting to start and so on. What else could it possibly be besides iac? I replaced tps and that wasn't it. So if iac is only other suspect I'll replace it.
 
#17 ·
Curious. Has anyone ever changed the IAC? What is recommended, general purpose Advance Auto part or OEM?

Mine does the same thing sometimes, I removed and cleaned the throttle body inside and out, including removing the IAC and cleaning it.

It helped for some time (maybe) but it did it again so I'm gonna start with replacing the IAC first.
 
#18 ·
Just unbolt, swap and bolt in. It has a rubber gasket/ORing on it you want to make sure is seated. And dont overtighten it. The housing is easy to strip.
 
#19 ·
Okay spent 1.5 hours at autozone trying different things. Started fuel fuel pressure. OR recommended is 31 I have 37. I replaced fuel pump fall of 2011. I also replaced the elbow fitting on both ends if vacuum line going to fuel pressure regulator tonight.

I took throttle body off cleaned it and the IAC. Both were filthy. Reassembled it and tps gave me a check engine light now(yes I removed both sensors prior to cleaning) I then put stock tps back in light goes away. Return tps.

After all this the jeep starts rough still but will idle almost immediately to 750-900 range. Ideas?
 
#21 ·
Couldnt a faulty O2 sensor cause it to run rich as well? If it is the downstream and he has an exhaust leak it could be detecting more air and giving it more fuel causing it to run rich. That obviously would be separate from the idle issue though.
 
#23 ·
Yes, but so should the TPS and IAC. The fact it is having problems and he wasn't getting codes for either of those is unusual as well. Normally without the code I would not suggest that, but I am going to assume for some reason he may not be getting all of the codes.
 
#24 ·
Just tuned it up 3 weeks ago today. On a side note started it up today and bam starts fine. The difference is it was raining when this problem started and has continued to rain until last night. Today it's not raining and started fine. Exhaust isn't clogged. I have to cat either just a flow master 40. I would think o2 would cause problems under also though. So I guess I will update this periodically through the day to see if I have issues.
 
#27 ·
sounds super similar to my problem. Did you find out what was the cause?

I gave it some gas when starting but that didn't really help start it. I did smell a considerable amount of fuel, which leads me to believe it is not the fuel pump. It just struggles to start. Cranks, fires, and gets oh so close to starting but just doesn't. Keeps trying continuously and sometimes it will start though with a high rpm idle (8-1200).
I did smell a considerable amount of fuel, which leads me to believe it is not the fuel pump.
 
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