99 Rodeo racing and stumbling/stalling

Recently, my 99 Rodeo (145K mi) has started to stumble and die at idle sometimes. Conversely, it races up to about 2400 rpm in neutral sometimes. It is either one or the other, no in between. Seems to run alright at speed.

OBDII check showed Mass Air Sensor code so I cleaned it up with throttle body cleaner. NO change so I replaced it with a new one. No change. OBD still show mass air sensor fault.

Also, sometimes it shifts at low speeds like a sledgehammer. Are there any engine speed sensors on the tranny (Auto/ 4wd) that could be contributing here?

Can anyone help me with this? Getting a little frustrating

Thanks to any and all who can help, Darwin

Intake manifold gasket leak? Check the FAQs.

I have read the FAQs and did look for vacuum leaks/manifold leaks. Doesn't seem like it really fits the picture either. WOndering if the the ECU is bad. The car had a tendency to race since I had it (4 yrs). The cure was to stop, shift into park and let the rpms settle down from 2300 to 900-1000. This took a couple of minutes.

I would agree that it is probably the intake manifold gasket.

sometimes you can check for leaks and you can't find them.

my IMG was replaced 2x within 72k.

intake manifold gasket. spray the cleaner around and if it gets sucked up it will change your idle. bout a 3 hour job, not bad.