Originally Posted by CathedralCub

Did you spray the MAF sensor with carb cleaner?

Originally Posted by CathedralCub

Are those fuel pressures from a real fuel pressure gauge or from the OBD2 telemetry?

Originally Posted by SailorJohn70

I have a 2005 Buick Rendezvous with a 3400 engine. We are the second owners. The first owners had all work done at a Buick dealership. We've owned it for about five years (65k miles). Our first repair about 6 month after we got it was a head gasket replacement. The car overheated and blew the gasket. Repair shop said it was a flaw in the HG design and the new gasket was "beef-ier". A few weeks later we started having problems with it not wanting to go at highway speeds [code P0300). Took it back to the repair shop they replaced plugs and wires and said they could not find anything wrong or recreate problem. A week later we started having the same problem again accompanied with difficult shifting. had a few repair places look at it but could not pinpoint the problem. We did find that if we only used high grade Non-ethanol fuel the power and P0300 did not have any problem, but it still did not shift well. Memorial day weekend 2019 the transmission gave out in Forsyth GA and we spent most of the week there waiting for the local shop to put a new tranny in it. The tranny seemed fine after that but with no non-ethanol gas in the area we started having misfires again. Octane booster and ethanol stabilizer added to fuel helped but still had to baby her on the interstate. the P030? codes only happened with a load at speeds above 60 mph (going up hill on interstate) and now we were also getting code P0101. We learned to keep high grade non-ethanol fuel in the car, not drive on the interstate, and not use cruise control. When we did need to drive on the big road and the problems popped up we could simply clear the codes (while driving ) and everything smoothed out. About a year ago I was pulling a trencher up our Tennessee Mountain (6% grade) and blew the transmission seal. The local shop replaced the seal and some other worn parts. Last week I was driving to Nashville (on the interstate) with little problems but as soon as I got off the Interstate the car started overheating at the first light. I did not have far to go and babied it there. Let the car sit for about 2 hours and then checked the coolant level it was low by about 12 ounces. I filled it up and started home. Driving the 3/4 miles to the interstate the temp gage would get hot then normal, hot then normal. I figured the thermostat was going out. Once I got on the interstate it drove fine at a normal temp, but as soon as I got off it started overheating again. I stopped and let it cool, the coolant level seemed good. I bought two bags of ice to pack the engine and radiator with and started the 30 mile drive home (I would have to climb over a 1000 feet up the mountain to get home) but on the flat I could only drive about a 1/4 mile before it would overheat. I pulled into a church parking lot and got a ride home and a friend helped me get the car home the next day. The car started and ran fine to drive it up onto the trailer, and then when we got home we unloaded the car about a 1/2 mile from my house and it drove home with no problems.

Thursday a pulled the thermostat (had to pull the intake and throttle body to get to it); put it in a pan of water and at about 180 degrees it started opening and was full opened by 195. I did notice a lot of coolant and residue coating everything under the throttle body and thermostat housing. I figured maybe I had a leek and/or air in the coolant system I got a new thermostat, new throttle body coolant hose, new throttle body gasket, and new bleeder valves. I also had to get new sparkplug wires because I broke the #4 plug wire tring to remove it so I could move the heater pipe to disconnect the throttle body. While I had everything apart I doused the engine with degreaser and cleaned the throttle body and intake with carb cleaner. I put everything back together and filled the coolant system and started to bleed the system. When I tried to start the car it would not start and was very rough turning over. It seemed like I got plug wires mixed up. I have checked and rechecked the plug wires and they are in the correct position. I've pulled wires for #* 2, 4,& 6 (the front three plugs) one at a time with no noticeable difference in how the car starts/runs. Ive, swapped #4 and #6 plug wires with no noticeable difference. I've pulled and checked all three coil packs (primary checks at .3 ohms, secondary checks at 6K ohms) the bottoms of the coils were slightly dirty/slimy/greasy but I cleaned them so they were clean and dry. There are no cracks, discoloration, or deformation on the coils or any electrical connectors I can get to. The back bolt on the coil packs were corroded both on the bolt washer and on the metal ring on the top of the bolt hole. I brightened both up with sandpaper and sprayed with battery corrosion inhibitor.
Nothing that I have done seems to make any difference at all in how the car starts or runs. It starts very roughly (insert your own expletive) with determination and pedal work I can get it to start and run then after about a minute or two the RPMs will kick up to about 3k and it will just sit there and race. I am not getting any codes from my OBDII reader.

What suggestions do y'all have for me?

Originally Posted by OldsManiac1990

you did something. it didnt just start doing this. ect connected?

Originally Posted by SailorJohn70

I agree, I have retraced my steps nine ways to Sunday and just can't figure out what it might be.

Originally Posted by OldsManiac1990

so where are you exactly nowwith your car

Originally Posted by OldsManiac1990

so where are you exactly nowwith your car

Originally Posted by SailorJohn70

nowhere! I don't know what to check next.