00 Explorer bucking at certain rpms

[cavedweller3366]

I have a 2000 explorer, 4.0 sohc, 2 dr. It has 103000 miles on it. I always change the plugs, oil, etc. Just recently I replaced the thermostat. I had to remove the air intake hose, tps, throttle body/flap, plenum gasket to get to it. Ever since doing this, the truck bucks at about 1600-1800 rpms. If I give a little exta gas or let up on the pedal, it stops. I retraced my steps and all looks correct. I'm not getting any codes. Any ideas? Thank you for your time.

[shorod]

Sounds like you probably missed or damaged a vacuum line or the intake air tubing in the process. With the engine idling you might try carefully flexing the intake air tube to see if you can get the engine to stumble. There's also the chance it's completely coincidental that it decided to act up now due to an intake manifold gasket or PCV elbow.

-Rod

[danielsatur]

Have a smoke test done for unmetered air leaks at a shop for $80.
I use Glad wrap around the air fiter to block air flow, blow smoke with with a Black &
Mild cigar through the vacuum hose from the Brake booster, and watch for leaks.

[brian_g]

Originally Posted by danielsatur

Have a smoke test done for unmetered air leaks at a shop for $80.
I use Glad wrap around the air fiter to block air flow, blow smoke with with a Black &
Mild cigar through the vacuum hose from the Brake booster, and watch for leaks.

I have the same issue, the bucking I mean. If it's the gasket like shorod suggested, you would be losing oil at the same time correct? I dunno what the PCV elbow he suggested is, but would that also mean you would lose oil? I've kept oil in my engine like it was brand new, but still have the bucking problem originally described. It's a new xplorer to me, I have not done any work except an oil change. I do know that the guy before me did replace the thermostat/water pump.

[danielsatur]

If no vacuum leaks, suspect a bad or dirty MAF sensor, or dirty throttle body.

[shorod]

There is no oil that goes through the intake manifold gasket, just air, which is why if that gasket fails, you get a vacuum leak. Similarly for the Positive Crankcase Ventilation (PCV) although this will support mostly air with combustion byproducts and some oily residue.

-Rod

[cavedweller3366]

So far I have replaced the IAC pump, cleaned the MAF sensor and thoroughly cleaned the throtle body/intake area. On a straight away, its fine, but on any incline or when kicking down a gear to make a pass, that is when the bucking occurs until I move the pedal around a bit, either increase or decrease. No codes, good gas mileage, no smoke, no oil loss. ??? Thanks for help so far gentelmen! Will keep at it.

[danielsatur]

Do a http://www.youtube.com/watch?v=FfiQ7qWiG-M

[cavedweller3366]

I finally got a code today and the bucking got a little worse throughout several rpms. The code is 442 Evap Emiss Control Leak (small). That is exactly how it appeared on the handheld OBDII reader my buddy has. Any ideas guys. Thank you for your continued support and time.

[cavedweller3366]

I found a small vacuum leak on top of the intake where the AIC bolts on. I removed the platform that holds the AIC pump, cleaned out area with throttle cleaner and coated with some gasket maker. Reassembled and done. Vacuum leak is gone....bucking is gone. Thanks so much for your help guys!