BIG Idle Issues

[Raptor660]

This is the first Jeep I've worked on and I'm still pretty new to these things, so any help anyone can offer would be much appreciated.

I just bought a 1999 Jeep Cherokee Sport with the 4.0 Inline Six for my girlfriend, only to find out the head gasket was leaking at the water jacket a few days later. So I tore the head off, had it milled, cleaned everything up and put everything back together.

Now that everything's back together, when it starts up the engine misses a little for about 2 seconds and then the idle jumps up like someone pounds the throttle down so I have to shut it off right away.

Things I've checked: Throttle cable adjustment, throttle assembly sticking, vacuum leaks and I tried replacing the throttle position sensor.. same thing.

I'm thinking it's either the MAP sensor or the coolant temperature sensor (seems weird) because they both tell the ECU how to regulate the fuel/air mixture.

The coolant temp sensor may have been sprayed with a little of that evil gasket dissolver stuff. Does anyone know what the inside end of those sensors are made of? Could that stuff have damaged it?

Any other ideas? Thanks for the help

 

[SteelHeadz]

The coolant temperature sensor housing is made of brass and some are plated. it takes more than a gasket dissolver to damage the sensor in that manner. That symptom seems to mimick a vacuum leak. if it was the coolant temp sensor then it would be a temperature related concern. I've seen this happen after a head gasket replacement, and what i've found was the intake manifold was not seated properly on the 2 dowels on the cylinder head causing a massive vacuum leak, thus the ECU commands the injectors to give it more fuel and you end up with a WOT(wide open throttle )condition. Recheck the intake manifold and double check the vacuum line connectors to it as well.

 

[Raptor660]

Thanks for the info. I'll check all the vacuum hoses and the manifold again. I could have sworn that when I started tightening that intake manifold, I heard both the front and back snap into place over those dowels... kinda freaked me out at first because I thought it was a bolt breaking.

Back out to the garage...

 

[SteelHeadz]

Thanks for the info. I'll check all the vacuum hoses and the manifold again. I could have sworn that when I started tightening that intake manifold, I heard both the front and back snap into place over those dowels... kinda freaked me out at first because I thought it was a bolt breaking.

Back out to the garage...

They are supposed to make a snapping sound when you tighten them.:shock:

 

[Raptor660]

They are supposed to make a snapping sound when you tighten them.:shock:

How right you were about the vacuum leak...

The snapping sound I heard wasn't quite what I thought (the manifold snapping into place over the dowels). The noise was actually the manifold cracking and breaking a nice large piece off right at the flange.

Nice catch on the vacuum leak. I thought I was fine after going over the hoses and everything a few times.. good thing I finally pulled the manifold.

Thanks for the help!

Off to buy MORE parts...

 

[SteelHeadz]

How right you were about the vacuum leak...

The snapping sound I heard wasn't quite what I thought (the manifold snapping into place over the dowels). The noise was actually the manifold cracking and breaking a nice large piece off right at the flange.

Nice catch on the vacuum leak. I thought I was fine after going over the hoses and everything a few times.. good thing I finally pulled the manifold.

Thanks for the help!

Off to buy MORE parts...

I'm glad you found it. make sure the dowels are clean from debris and burrs before you install a new manifold. good luck.

 

[SteelHeadz]

Mopar t's, haha, get it?. j.k.

 

[Raptor660]

Mopar t's...lol.

The wonderful Jeep dealer finally graced me with an intake manifold... and it even went back together with no snapping sounds this time. I sure wish Edelbrock or someone made a decent after-market intake for these motors, because I bet it would be cheaper than what I just paid for the factory part. On a positive note, I've had to special order so much crap from those guys they don't even make me pre-pay anymore..lol

Back to the garage... let's see what explodes this time.

 

[SteelHeadz]

Mopar t's...lol.

The wonderful Jeep dealer finally graced me with an intake manifold... and it even went back together with no snapping sounds this time. I sure wish Edelbrock or someone made a decent after-market intake for these motors, because I bet it would be cheaper than what I just paid for the factory part. On a positive note, I've had to special order so much crap from those guys they don't even make me pre-pay anymore..lol

Back to the garage... let's see what explodes this time.

Just remember, don't let the bolts pull the manifold to the cylinder head using your hand tools or air tools. while gently applying a little push and a little wiggle of the manifold to the cylinder head, snug the bolts with your fingers and double check that the Dowels are in the maniflod holes ALMOST flush. then use your hand tools to tighten the bolts.

 

[Raptor660]

Just remember, don't let the bolts pull the manifold to the cylinder head using your hand tools or air tools. while gently applying a little push and a little wiggle of the manifold to the cylinder head, snug the bolts with your fingers and double check that the Dowels are in the maniflod holes ALMOST flush. then use your hand tools to tighten the bolts.

I never use air tools for this kind of thing, mainly because my tool collection isn't quite what it should be anymore...lol

It looks like the first time around, the rear dowel slipped out before I had any bolts snug. This time, since I couldn't fit my head down in there to see, my girlfriend took a picture of it with a digital camera while I held it in place so I could see for sure.

Everything went back together like butter, now that I've replaced almost everything under the hood. The previous owner who took "excellent care" of it torqued almost every bolt in every bracket or part to over 100-ft lbs. Nothing like trying to get the cylinder head off while everything you touch snaps and breaks!

The guy at the Jeep dealer Parts Dept loves me though. I bet the commissions he's made off me in the last 30-days have paid all his bills this month..lol I was surprised to see how many parts I couldn't find anywhere but the dealer (aside from salvage yards, of course).

I'm off to pickup the VERY LAST (you hear me Merle's?) set of spark plugs, and this baby better purr like a kitty.

 

[Raptor660]

So now that it runs for more than 5 seconds, the trouble codes finally come through and tell me about all the sensor errors indicating the previous vacuum leak at the intake manifold. How helpful! Good thing I bought the stupid OBD II scanner since it cost more to RENT than it did to buy.

::ERASE CODES::

::START ENGINE::

Never been so happy to hear a smooth running inline six. Now all that's left is one more oil & coolant flush to get all the crusties out from the head being off.

Oh, and then the U-joints... and the lift... and the tires & wheels... and the exhaust. Maybe this is still just the beginning...

Now comes the sad part... after about $3,000, 3 weeks of work, at least a good pint or so of blood, and countless packs of smokes... I have to give the Jeep back to my girlfriend... and then sell my truck so I can get another one. HA

 

[SteelHeadz]

Now comes the sad part... after about $3,000, 3 weeks of work, at least a good pint or so of blood, and countless packs of smokes... I have to give the Jeep back to my girlfriend... and then sell my truck so I can get another one. HA

I WAS going to ask where you found a girlfriend willing to work on the Jeep with you, Now that i know WHY she helped, Nevermind. Good luck selling your truck.:lol::lol:
Oh BTW, Congratulations on a job well done, i'm glad it's running, eventhough your going to loose it.(just thought i'd rub it in)