Surging Idle

[Research Rat]

So I just noticed that when truck is idling in neutral, the idle surges from 10-15 seconds at 600 rpm to 900 rpm for 5 seconds, then repeats at a fairly regular interval.

I do not notice any surging once moving.

Plugs, plug wires, and pcv valve were changed about 1500 miles ago-so fairly fresh.

Any thoughts on steps to start troubleshooting?

TIA.
-Scott

 

[TheTopher]

Clean out your IAC valve

 

[Research Rat]

TheTopher,
What is and where would I find the IAC valve? And how would you recommend cleaning it?

Thanks!
-Scott

Clean out your IAC valve

 

[modelageek]

TheTopher,
What is and where would I find the IAC valve? And how would you recommend cleaning it?

Thanks!
-Scott

go to rockauto.com and and look the part up to see what it looks like, it is about 4" long and looks like a mini biscuit-joiner(if you are a wood worker). it is attached to the throttle body. there are 2 bolts holding it on. remove it it has a motor at one end and an open cavity with a rubber seal that allows air to flow. clean out the cavity with maf cleaner or equivalent. get a new gasket if possible. you should clean off the MAF also. Do you have the cel on? did you check for codes?

*make sure you air intake is clear and the air filter is good

 

[kimcrwbr1]

If you clean the maf disconnect the battery for 1/2 hour and then run it for about 20 mins to reset the computer to new values.

 

[Research Rat]

Hey Modelageek,
Thanks for pointing out the site, I have a good idea of the part now.

You posted some other info that I'm not familar with.

What is the cel?

I have not checked for codes since I don't have a code reader-do you know if you can you borrow one from an autozone or similar?

I replaced the air cleaner with the oil change which was just a few hundred miles ago-so this should be good.

-Scott

go to rockauto.com and and look the part up to see what it looks like, it is about 4" long and looks like a mini biscuit-joiner(if you are a wood worker). it is attached to the throttle body. there are 2 bolts holding it on. remove it it has a motor at one end and an open cavity with a rubber seal that allows air to flow. clean out the cavity with maf cleaner or equivalent. get a new gasket if possible. you should clean off the MAF also. Do you have the cel on? did you check for codes?

*make sure you air intake is clear and the air filter is good

 

[disciplerocks]

IAC or vacuum leak are your most common problems.

If you clean the maf disconnect the battery for 1/2 hour and then run it for about 20 mins to reset the computer to new values.

x2 definitely do this. And make sure a/c and defrost are off.

 

[TheTopher]

Looks like everybody else beat me to it. lol

Anyway the CEL is check engine light. Autozone will pull the codes for free.

 

[Research Rat]

Ah, no check engine light. Oil light has come on a few times though-didn't think they were related...

Good to know about AZ pulling the codes.
-Scott

Looks like everybody else beat me to it. lol

Anyway the CEL is check engine light. Autozone will pull the codes for free.

 

[Research Rat]

I found the culprit: the defroster was on.

A friend with the same truck pointed it out to me the other day, with the defroster on, the idle surges (ac pump on?) like clockwork mentioned above.

With defroster off, idles as should.

I'm assuming this is normal?
-Scott