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Rough idle=Vacuum leak?

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FullNelson

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My 89 blazer seems to have developed a bad idle when cold or left off for more than about an hour. I've troubleshooted around, and when I went to test the MAP, at atmosphere, it was at 3.5v. Yet the brand new parts store replacement speced the same. Is this coincidence, or is this not my problem?

Altitude is about 6200'.
 
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Change the TBI gasket, seems to be a pretty common failure point. Once you have a new gasket and can eliminate that as the culprit then continue. I doubt it's the MAP sensor (had one go bad once and there was no giving it throttle at all before it would die). Check to make sure the vacuum hose hooked to it is clear and is infact hooked up to the rear fitting on the TBI unit.
 
NO RTV, you need to replace the gasket with a new one and NO SEALER.
 
The gasket looked good, with no visible damge as far a a gasket goes. (Do these gaskets need a visible rip or other damage to fail?) I replaced the gasket and will do a final torquing and await results when the motor cools to closer to ambient temp. The front bolt was very loosely fitted, While the other two were closer to 20 ft#s.
 
Idle will usually be OK if MAP is bad.
Check all vaccum lines and EGR as said above. May also have a bad coolant temp sensor telling the ECM that the engine is warmer than it really is causing it to idle bad when cold.
 
EGR valve is good. It was bad and threw a code for that and a 44 (lean o2). Solenoid is questionable, however there is no change in idle when it is capped.

I am going to guess a vacuum leak as well because it idles great when the MAP is disconnected.
 
Fuel filter and pressure are unknown. If it were fuel pressure I would expect to see it run rougher at a higher RPM.
 
throttle position sensor was bad on mine and causing me to get a map sensor error code. would rough idle and stall on me
 
TPS was checked and seemed good with no jumps in voltage. I believe remembering that idle was a little high, like .63v, and WOT was a little low, 4.3v.

Today I had a code 44 trip the CES light when driving. Im leaning toward it being vacuum leak on account of it running fine WOT.
 
What would be the steps for finding a vacuum leak?
Start off with plugging all the ports for MAP, EGR, emissions canister. If that doent change the idle, then It would be the intake to head gasket? Where are the lines run from on the motor for the defroster? What all are places I should be checking for leaks from?
 
The most probable for a vacuum leak would be any of the vacuum lines. Also don't forget to test the power brake booster, most people overlook that and run in circles trying to find a problem only to have a bad booster.

It is very doubtful of an intake gasket leak causing your problem. Most times when there is a problem with an intake gasket it is water leaking at any of the 4 corners because the bolts are loose or electrolisys as erroded the manifold.
 
Well after looking at all five vacuums, the one from the MAP to TB was bad, so Its been replaced. I plugged the brake booster line as well and didn't really notice any difference.

Now Im getting a fairly consistent (but sparadic) code 44, lean o2. The bogging is still there at odd times too.
Ive also noticed the top portion of my ECU temp sensor has broken to be flush with the wiring connector, It will still hold its self on and stay connected, yet I know any reasonable bump could dislodge it.
 
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