Rough Idle on Cold Start - JeepForum.com
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post #1 of 16 Old 02-28-2008, 11:52 AM Thread Starter
rugbynut
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Rough Idle on Cold Start

Well I finally finished my head gasket job and minor overhaul. I fixed, cleaned, replaced, and rebuilt everything that I could in the process of doing the tear down to the head. New seals, gaskets, plugs, and any other replaceable bits that I could think of along the way. I put everything back together over last weekend and was ecstatic to fire the Jeep back up on Sunday. It ran better/quieter, idled smoother, and had more throttle response than it has since I have owned it. I took the wife and kids for a cruise and everybody was happy.

As of yesterday the honeymoon is over.

The last couple of days we have had pretty cool mornings. Both days the Jeep has started fast and easy, but then begins to idle really rough. It sort of idles fine for second-then drops rpm/idle-then back up-then back down...cyclically in an even rhythm. It never dies, but sounds like it could. If I drive it cold, it never really stumbles or has any hesitation. At higher RPMs it sounds/runs fine. But at a stop sign or light, it sounds rough again...UNTIL it warms completely. After the 5 mile ride to my sons school at about 60MPH, it runs and idles smoothly once again.

I've done some searching around and found a few different ideas. From the sound of other people's posts/problems, I would bet on vacuum problem if it had happened right off of the bat. But it didn't, it started with colder/denser air. I am focusing my suspicions on TPS or temperature sensor on the the throttle body?

Although I cam here to see if anyone else had similar problems, other suggestions or thoughts. As always any help would be appreciated. TIA.


I love my Jeep, it just doesn't love me back.
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post #2 of 16 Old 02-28-2008, 12:30 PM
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Have you checked the engine codes?

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post #3 of 16 Old 02-28-2008, 01:37 PM Thread Starter
rugbynut
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Quote:
Originally Posted by Brown Dog View Post
Have you checked the engine codes?
Nope. As part of my general ignorance and noobishness to Jeep mechanical work, I have only ever checked codes (once years ago) when the check engine light came on.

I have seen several threads, and printed the codes. I will try this tonight. Thanks.

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post #4 of 16 Old 02-28-2008, 05:08 PM
jay-h
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I got mine after a head gasket replacement. I had cold idle problems for months till I found out that they had failed to tighten one manifold bolt. Check all your bolts and condition of the gaskets.
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post #5 of 16 Old 02-29-2008, 10:46 AM Thread Starter
rugbynut
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Quote:
Originally Posted by jay-h View Post
I got mine after a head gasket replacement. I had cold idle problems for months till I found out that they had failed to tighten one manifold bolt. Check all your bolts and condition of the gaskets.
Thanks for the suggestion. If I hadn't done this job completely by myself, I would think this could be it. I put the manifolds back on the head prior to reinstalling all of it as one piece. I did it on my workbench and torqued them to spec.

Then again, I'm not above second guessing myself so I will check them.

What is killing me is how everything ran great for 2-3 days and then all of a sudden got crappy.

I love my Jeep, it just doesn't love me back.
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post #6 of 16 Old 02-29-2008, 10:58 AM
Brandon_YJ
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Quote:
Originally Posted by rugbynut View Post
What is killing me is how everything ran great for 2-3 days and then all of a sudden got crappy.
That would lead me to assume that you did do it right (tightening the bolts) and one worked its way loose.
It's a possibility.
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post #7 of 16 Old 02-29-2008, 04:20 PM Thread Starter
rugbynut
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OK, I haven't checked my codes or rechecked my manifold bolts yet. BUT, I did discover something interesting today.

The 'oil cap' that came with my new valve cover is gone. Yesterday, I noticed it was loose when I was inspecting vacuum lines. I saw that the cap looked like it was barely sitting in the opening. I took it out wiped it off and replaced it firmly. Today at lunch, I went out to the Jeep and it would barely start much less hold cold idle. BTW it's 70-ish degrees here today. I gave the Jeep a pump on the gas pedal and got it started. I let it idle for a few minutes until it held idle on it's own. Then I got out and looked in the engine compartment, and this time the oil cap is gone.

I ordered this valve cover from Q-Tec and have had nothing but trouble with it since I got it. First, the original one that I ordered cracked on tightening the bolts down to torque specs. The Q-Tec people couldn't have been any nicer and shipped a new one out very fast. They blamed a manufacturing defect and that was the end of that. The new one came, I installed it exactly the same way. No cracks, and I was happy. Kind of.

One thing that I never liked, was how cheesy and cheap the oil cap they sent with the valve cover has looked. It is the crappiest little rubber plug that has the word oil on it. It is not grooved or notched to lock down or seal tightly like the OEM ones. For that matter, neither is the valve cover opening. The plug is simply a rubber stopper that sort of pushes down into the hole that is cut into the valve cover.

Could this be the root of my problems? Can a poorly seated/sealed oil cap (now missing) be causing my idle problems or is it just coincidence?

I love my Jeep, it just doesn't love me back.
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post #8 of 16 Old 02-29-2008, 07:47 PM
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I took a look at the Quadratec cover and it doesn't look right.
Your original cover had slots for the oil cap and the CCV fittings.
If the CCV orifice that goes in the rear of the cover isn't seated and sealed properly it may explain the oil cap blowing off due to the build up of crankcase pressure.
Also if the CCV fittings don't fit properly it could cause a vacuum leak and confuse the PCM as far a fuel mixture goes.
Compare the openings on your original cover to the new one.
Quote:
Originally Posted by rugbynut View Post
OK, I haven't checked my codes or rechecked my manifold bolts yet. BUT, I did discover something interesting today.

The 'oil cap' that came with my new valve cover is gone. Yesterday, I noticed it was loose when I was inspecting vacuum lines. I saw that the cap looked like it was barely sitting in the opening. I took it out wiped it off and replaced it firmly. Today at lunch, I went out to the Jeep and it would barely start much less hold cold idle. BTW it's 70-ish degrees here today. I gave the Jeep a pump on the gas pedal and got it started. I let it idle for a few minutes until it held idle on it's own. Then I got out and looked in the engine compartment, and this time the oil cap is gone.

I ordered this valve cover from Q-Tec and have had nothing but trouble with it since I got it. First, the original one that I ordered cracked on tightening the bolts down to torque specs. The Q-Tec people couldn't have been any nicer and shipped a new one out very fast. They blamed a manufacturing defect and that was the end of that. The new one came, I installed it exactly the same way. No cracks, and I was happy. Kind of.

One thing that I never liked, was how cheesy and cheap the oil cap they sent with the valve cover has looked. It is the crappiest little rubber plug that has the word oil on it. It is not grooved or notched to lock down or seal tightly like the OEM ones. For that matter, neither is the valve cover opening. The plug is simply a rubber stopper that sort of pushes down into the hole that is cut into the valve cover.

Could this be the root of my problems? Can a poorly seated/sealed oil cap (now missing) be causing my idle problems or is it just coincidence?

All other things being equal, the simplest solution is the best.
Ich liebe meinen Jeep!
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post #9 of 16 Old 03-01-2008, 08:35 AM Thread Starter
rugbynut
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Quote:
Originally Posted by pat8942 View Post
I took a look at the Quadratec cover and it doesn't look right.
Your original cover had slots for the oil cap and the CCV fittings.
If the CCV orifice that goes in the rear of the cover isn't seated and sealed properly it may explain the oil cap blowing off due to the build up of crankcase pressure.
Also if the CCV fittings don't fit properly it could cause a vacuum leak and confuse the PCM as far a fuel mixture goes.
Compare the openings on your original cover to the new one.
This is the one that I bought. The rubber grommets for the CCV system were a pain in the butt to get in, but once they seated they seemed fine. I bought this CCV elbow for the rear and this one for the front. It seems like kind of an all or nothing deal. They are either in or not. If I set it up right, then I would guess it should be working right.

I am going out to play around with the Jeep, so I came to check any suggestions that might have been offered.

I love my Jeep, it just doesn't love me back.
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post #10 of 16 Old 03-01-2008, 08:54 AM
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The rear elbow is supposed to have a metered orifice in it so that my be part of your problem as the NAPA one is just straight through.
Quote:
Originally Posted by rugbynut View Post
This is the one that I bought. The rubber grommets for the CCV system were a pain in the butt to get in, but once they seated they seemed fine. I bought this CCV elbow for the rear and this one for the front. It seems like kind of an all or nothing deal. They are either in or not. If I set it up right, then I would guess it should be working right.

I am going out to play around with the Jeep, so I came to check any suggestions that might have been offered.

All other things being equal, the simplest solution is the best.
Ich liebe meinen Jeep!
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post #11 of 16 Old 03-03-2008, 10:13 AM Thread Starter
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Quote:
Originally Posted by pat8942 View Post
The rear elbow is supposed to have a metered orifice in it so that my be part of your problem as the NAPA one is just straight through.
One of the NAPA ones is straight through, one is not. I bought one of each of the linked ones.

Looking at my engine, the one that connects to the front of the valve cover, and goes to the air filter, looks straight through. The other one, in the rear, is the one that NAPA labeled as "w/ orifice". Is this not right? I basically followed this configuration from my old (OEM) valve cover. It appeared to be set up that way also.

I did a little testing yesterday and did find that if I disconnect the rear tube off of the elbow with the orifice, that the engine idle immediately picks up and the Jeep runs much better. If I put my finger over the vacuum hose it chokes out again. So it would appear that the elbow I bought is not right in some shape or fashion, because it seems to not be letting enough air through the orifice.

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post #12 of 16 Old 03-03-2008, 11:07 AM
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Does the new valve cover have baffles where the CCV elbows go?
If you look in the hole and see the rocker arms it doesn't if you can't than it does.
Quote:
Originally Posted by rugbynut View Post
One of the NAPA ones is straight through, one is not. I bought one of each of the linked ones.

Looking at my engine, the one that connects to the front of the valve cover, and goes to the air filter, looks straight through. The other one, in the rear, is the one that NAPA labeled as "w/ orifice". Is this not right? I basically followed this configuration from my old (OEM) valve cover. It appeared to be set up that way also.

I did a little testing yesterday and did find that if I disconnect the rear tube off of the elbow with the orifice, that the engine idle immediately picks up and the Jeep runs much better. If I put my finger over the vacuum hose it chokes out again. So it would appear that the elbow I bought is not right in some shape or fashion, because it seems to not be letting enough air through the orifice.

All other things being equal, the simplest solution is the best.
Ich liebe meinen Jeep!
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post #13 of 16 Old 03-03-2008, 11:15 AM Thread Starter
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Quote:
Originally Posted by pat8942 View Post
Does the new valve cover have baffles where the CCV elbows go?
If you look in the hole and see the rocker arms it doesn't if you can't than it does.
Yeah, it has baffles.

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post #14 of 16 Old 03-03-2008, 11:24 AM
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Sorry, I'm out of ideas.
Quote:
Originally Posted by rugbynut View Post
Yeah, it has baffles.

All other things being equal, the simplest solution is the best.
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post #15 of 16 Old 03-04-2008, 03:34 PM
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Originally Posted by rugbynut View Post
Thanks for the suggestion. If I hadn't done this job completely by myself, I would think this could be it. I put the manifolds back on the head prior to reinstalling all of it as one piece. I did it on my workbench and torqued them to spec.

Then again, I'm not above second guessing myself so I will check them.

What is killing me is how everything ran great for 2-3 days and then all of a sudden got crappy.
Recheck and re-torque the manifold bolts.That is specified after the engine has reached operating temp. Some manufacturers also specify re-torquing the head bolts.
If you want to check whether the manifold is leaking, spray some brake cleaner fluid around the mating surfaces of the manifold while the engine is running.If the engine runs better,you have a leak. That tip is from Hesco who know their stuff around engines.
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