Thread: Really.... laggin, now over heating, and tach reading 20 mph higher than actual speed

New to the grand prix family, always been a bit fascinated with the cars. So I just picked up a 2008 very clean, and drove great for the 4 hours we were test driving....then we go home

I suddenly get a 'Reduced Engine Power' car begins to lag, doesn't want to pick up, very slow on reaction. This happens occassionaly not a constant problem; but I'm sure if I don't correct the issue it will become a bigger problem (problem #1)
Husband takes it to get the code, comes back with an explanation and no code so I am going today to get the codes (problem #2)
Driving to work today, much better no lag....then I notice I'm driving slower than everyone around me in a 55 MPH zone, and the car is telling me it's going 85 MPH; get to my office and park....car states it's going 20 MPH while in park. - restart the car, needle gets stuck at 80 MPH while in park, restarted again, no change... waited a minute, restarted, finally read correctly. (problem #3)
over heating, not majorly bad but always a concern, noticed yesterday after driving 80 miles while in stop and go traffic, I arrive home, open my gate and get in the car, and the needle has gone up; pull into the drive wait to see if it climbs, slightly climbs and then slowly start to go back down (problem #4)

With the exception of #2, I'm not sure if they could all be related or seperate, or any ideas from any one on what I'm looking at here...

Welcome to the forums!

These cars run hot even on a good day. How hot are we talking here (on the gauge)?

Check the battery connections for corrosion and tightness. Might want to pop them off and clean them up real good then tighten. I've seen loose/corodded cables do strange electrical things to these cars.

And definetly grab the codes.

Transmission temp was about 200 heard they run about the same

Well, the temp sounds about right.

That is a list of codes, lol... Off hand the TPS looks like it may be suspect, along with the front O2 sensor. Being an 08 it may be a good idea to remove the entire throttle body and all the sensors and then clean it until it shines, then clean the MAF w/ approved MAF cleaner spray and then see what you get. The TB's get gunked up on the DBW systems and cause all kinds of wierd issues. Best of all it's the cheapest thing you can start with w/o replacing parts.

The rest I'm not sure on. Maybe try a quick search for those other codes and see what comes up in other threads.

Checked fuses found only 2 bad, no difference, chsnging out the 02 sensors and the tbp....just a note, when I get the engine power loss (once a week) I lose cruise control and mph is way off. Hsve to retart car 2 x times for every thing to go back to normal.

I don’t know if this helps.
Is 'Reduced Engine Power' the same as "Limp Mode"??
I don't know if the '08 GP transmissions have a Transmission Control Module(TCM) or "Input/Output Sensors" also called "Speed Sensors(not the ABS Speed Sensors)".
My '00 Dodge Intrepid had them.
When the input sensor goes bad, the car will only drive in 2nd gear("Limp Mode").
When the output sensor goes, the speedometer will not work.
I tried doing a search for a TCM and I/O Sensors for an ’08 GP.
The only thing that came back were speed sensors for ABS.