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Dodge Repair/Erratic engine idle (COLD)

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Mr. Finston,

Let's take it from the top!  2004 1500 RAM 4.7.  

First--this truck had a large leak in the evaporative system, and was driven that way for quite some time.  That issue--a broken nylon tube on one of the fuel tank rollover valves--has been corrected, via replacement of the fuel tank.  There are no codes anymore reflecting any issue with the evaporative system.

Second--this truck was having a "warm shutdown" issue i.e., wouldn't start for 10-15 minutes.  The fuel pump turned out to be the culprit (excessive fuel pressure/previous mechanic let dirt/debris fall into tank, among other sins).  That's all been taken care of with replacement of the fuel pump.  There haven't been any no-start situations since replacing the fuel pump.

Finally, there's just one problem left--and, I hope you can help me.  This truck when started cold, for a brief moment or two, idles erraticly.  Too high ... up and down a couple of times and eventually straightens up.  No idle issues, at all, as engine warms up to operating temperature.  There's just this "issue" when first starting the engine cold.  No codes.  Never any codes other than the one about the large leak in the evaporative system.  That code was cleared some time ago and nothing else since.  

Yesterday, I did R&R the IAC (cleaned the hole in the throttle body etc. with no change.  Additionally, one of my first acts with this vehicle involved cleaning the throttle body with a full can of spray cleaner, while the engine was running. The throttle body is clean as a whistle, although I admit I didn't scrub the throttle blade edges, or the throttle bore.  Your thoughts?

Answer
Hi John,
A brief rough idle issue at cold startup suggests some sort of a mixture problem no doubt related to excess air getting into the manifold from a non-monitored pathway. Your suggestion about the throttle plate edge, the throttle throat, and actually both sides of the entire throttle plate all needing to be clean would be the first thing to focus upon. Then I would check all the vacuum hoses for possible cracking or poor connection at their ends, using the under side of the hood diagram as the guide. All the sensors on the intake manifold should be checked for tight retaining screws.  In the absence of codes it will be something subtle.
The engine coolant temp sensor and the intake air temp sensor (mounted on the left side of the manifold, dark blue/dark green, dark blue light green wires) should be measured for their resistance when the engine is cold. They should show very similar readings and then move to lower resistance as the engine warms up (but not to identical values when warmed of course).
Those are my suggestions for what to do next.
Thanks for the rating and nomination!
Thanks,
Roland  

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Roland Finston

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Get a Free Fast answer to your repair question about a Chrysler/Dodge/Plymouth car, minivan, SUV, or truck. Problems with electronically controlled engines and transmissions as well as body wiring problems are my specialty. This free troubleshoot advice forum helps you diagnose faults, minimize repair costs or do-it-yourself.

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Five decades as a 'do-it-yourselfer' on domestic and imported cars

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Yahoo Autos Group called The Chrysler Lebaron Club (co-moderator)

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Degrees in Physics/bruised knuckles.

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"Top expert" of 2010, 2011, 2012, 2013, 2014, and 2015 here at Allexperts. Quickest "average response time" at Allexperts (currently no. 1).

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