Hello, I need some help with my 2006 Buick Rendezvous. I am a recent college graduate and do not have a lot of money to take my car in and pay for diagnostics and repairs so I made the decision to attempt my own repairs.
Anyways, my Rendezvous has 86,000 miles on it and is a V6 3.5L engine. Recently (about 3 weeks ago) I started to experience sluggish performance (very slow acceleration especially while going up hill), what I think are misfires (rpms will flicker up and down) and I think decrease mpg but with no check engine light. The issue would only happen between 2000 and 3000 RPM and would be especially apparent when taking off from a red light. The car wouldn’t stutter below 2000 RPMs and above 3000 RPMs and it would only occur when the engine was warmed up, it ran perfectly when i would just be start driving. So I did some research and ended up changing the engine air filter (which was filthy) and cleaning the MAF sensor with MAF cleaner. After that the engine ran much better pretty much immediately; it was no where near as sluggish and the stuttering disappeared. That was about 2 days ago and pretty much right after I started experiencing RPM surges and drops when I would try to accelerate hard. This usually only happens around 3000 RPM and only when the engine is warm. If I would step on the gas hard the RPMs would remain stagnant for a couple of seconds like it is taking a second to register and then the RPMs will shoot up to 5000 RPM until I left off the gas and then it falls. At no point during this problem have I had any problems or misfires at idle or in neutral while stepping on the accelerator, only while driving. I was wondering if anyone had any suggestions on how to fix the surges and drops? I called a mechanic and they told me the spark plugs should be fine since they’re iridium and I have 86,000 miles but I havent checked them myself since I’m just starting this whole diy repair thing.
Other important notes: I had my transmission rebuilt about 5 months ago and it ran absolutely perfect until 3 weeks ago. I also had a problem with the EGR valve lighting up the CEL but the people that fixed my transmission told me some of the wires to the EGR valve were damaged and after they repair those the CEL hasn’t come on since.