RPM jumping under high engine load

[crzymazy]

Hey guys, first post here! been a lurker for quite a while, trying to get this car of mine into tip top shape (2000 Pontiac Grand Am SE). Ive been experiencing this problem where the rpms will jump while the engine is under a high load. If i apply more throttle, the problem goes away.(as shown in the video)


I was wondering if anyone has experienced a similar problem? In the youtube video below, i am going up a 5% grade. This will happen at slower speeds, but i will need a significantly steeper grade of around 25-30% (abundant in seattle lol)

[dreager]

Had this happen for 4 months and thought it was an EGR issue which i was dealing with. (egr pipe rusted out etc.) It was a dirty MAF sensor! Car runs like a top since and getting better gas mileage.(8+/gal) Check air filter while in there. Be very careful cleaning it as they are delicate wires,best use MAF cleaner spray. Lots of videos on YouTube.

[crzymazy]

Hmm, I've tried most of those things. I cleaned the mass airflow sensor with appropriate cleaner,( verified that i got reasonable readings with a scan tool *to clarify, the sensor gave a linear response,I didn't compare the value to whatever the specs should be*) replaced air filter, replaced plugs, wires, replaced fuel filter. TPS was giving me appropriate readings with scan tool (but I haven't checked the actual sensor with a multimeter) checked all vacuum lines and fixed a few rotten ones. Replaced PCV valve (i discovered it was faulty when I cleaned the mass airflow sensor and throttle body was found grimy with oil). Before I replaced the vacuum tubes, I took a reading with a vacuum guage and on startup, vacuum was at 17 in mercury slowly climbing to 20in mercury. None of the leaks I fixed were terribly large, just cracks in some hoses. Still plan to take a fuel pressure reading on the rails while im driving and recreating the behavior. I'm starting to think that it may be a lack of hydraulic pressure in the transmission due to the Surge of acceleration when the rpm drops. Hopefully there's a sensor I can tap into with my scan tool. Thanks for the reply!

[gmtech1]

Can you actually feel the RPM change, or is the tach just jumping? Have you verified the RPM change with a scanner? Just some questions for info...

[crzymazy]

I haven't checked the rpm with a scan tool while driving, that will be my next check. However I can hear the engine's tone go up and down in sync with the rpm guage. Whenever the rpm drops, a slight but sudden acceleration is felt. Since there is no gain of speed during this, I assume that I'm decelerating when I don't feel that "jolt".

Thanks for the reply, im beginning to think this problem will get the best of me..

[crzymazy]

I'll upload some plots of rpm, transmission hydraulic pressure( if available) and anything else I find relevant. Please suggest other parameters that I should monitor if anyone has some ideas. Thanks!