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4.0 Rough Idle


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1988 Jeep Comanche, 4.0, 5 Speed, 2wd. I've had it for a few months, did plugs, wires, cap, rotor, water pump, and some other maintenance when I got it. Its been running good, but had an oil leak, and clutch slave cylinder was going out. So this past week I did pilot bearing, slave, rear main, and oil pan gasket. While it was apart, I noticed the crank position sensor wire was burned up. I cut the burnt a action out and soldered new wire in. I got it all back together last night, and now it has a horrible rough idle. Under load it will smooth out, but at idle its bad. Slow down to come to a stop at a light and it dies sometimes. When idling, it sounds like it has a miss.

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I remove the throttle body and tap the lower hole on it to 1/8" NPT thread and plug it. 

 

I move the IAT to the upper half of the air cleaner.

 

I then install a fitting in the intake manifold that will accomadate a hose/pipe to run to the MAP sensor. 

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So what good does that do? The MAP is still up on the firewall where the vacuum hose/pipe can be broken, knocked off, or leak. Too bad you don't have an HO where excess vacuum lines can be eliminated and the MAP can easily moved to the throttle body, where it should be. BTW, the 96 HO MAP is the same as the Renix MAP; would be a good Renix tip to figure how to mount it on the funky Renix throttle body. Or at least get if off the firewall.

 

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Being that the MAP didn't move to the TB until what ... 2000? What makes that such a big HO selling point?

Change the plastic line for a piece of 3/16" brake line bent to suit and never break it again. If it broke, it was because it was brittle and needed replacement anyway.

As for mounting one to the TB ... easy ... Drill a hole below the throttle plate through the TB body. Hammer in a small section of brass tubing. Make a bracket to index off the rubber air hose bolts. Mount MAP on that bracket and run short section of hose to new TB nipple.

Even us Renix guys can figure that out ... but it also begs the question ... Why? Other than protection from inattention around old crusty parts, is it going to make any difference?

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The bottom elbow on the MAP is just a rubber elbow. Would actually be fairly easy to move to the TB on both a Renix and an earlier HO.

And, I totally gapped ... Tap the stock MAP port, run a nipple there, and mount off that side of the TB. A simple bracket can be made to hang off the IAC bolts and wrap around to wherever.

Even easier that doing it on an early HO.

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The bottom elbow on the MAP is just a rubber elbow. Would actually be fairly easy to move to the TB on both a Renix and an earlier HO.

And, I totally gapped ... Tap the stock MAP port, run a nipple there, and mount off that side of the TB. A simple bracket can be made to hang off the IAC bolts and wrap around to wherever.

Even easier that doing it on an early HO.

Gonna need to lengthen the MAP wires I bet. 

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