jakemussman

iTrader: (3)

Im having a random car problem, my car seems to want to drive itself. Its a 90 3.1L Auto. At cold startup idle is around 1000-1100. When warmed up its between 700-900. while driving sometimes my car behaves as if cruise control is on. It wants to stay around 2000-2100 RPM and between 20-30MPH. This is with my foot off the pedal of course. If i come to a stop or use the brakes idle drops to 1100 and bogs down. It has yet to cut out yet. I replaced the TPS and that didnt help. I checked timing and its good. It usually dosent code when this happens. I checked for codes anyways after one incident and it was 33. I remember it was low vacuum detected at MAP, that made sense. I then checked for vacuum leaks and couldnt find any. I then bought a vacuum gauge and checked vacuum. It was around 18-18.5, I know this is a little lower then desired. The gas peddle isn't getting caught on anything. The throttle blade opens and closes fine with out binding or catching. Again this happens randomly and usually will go away if I pull over and shut the car off and restart it. Also, these may not be related but I am getting poor fuel milage and my car never wants to get upto operating temperature.

Any ideas?
Thanks, Jake

zraffz

Vacuum... get a can of ether and start spraying the engine bay.

jakemussman

iTrader: (3)

optimal is around 19.5cfm im sitting at around 18.5cfm. would that small of a variance in vacuum cause this?

ASE doc

Definitely check carefully for vacuum leaks. Also, the 2.8 and 3.1 had a common issue with worn throttle shaft bushings. Check the throttle carefully for any lateral movement in the shaft. Checking TPS voltage can be helpful in diagnosing this. Cycle the thottle open and closed several times, looking for small variations in closed thottle voltage from one cycle to the next. Verify engine temperature with an infared thermometer and compare the readings with CTS as seen by the ECM.

jakemussman

iTrader: (3)

I really didnt want it to be a vacuum leak but everything is pointing towards it. Im pulling less Cfm's gradually it seems. The good news is the sputtering anytime I came to a stop has stopped. Now I just have the idle fair up at startup and the rpms bounce pretty low when breaking. My vacuum lines are in good shape and do not seem to be leaking. The car has always made a whistling noise as well. So today after work I am going to pull the entire intake and replace all of the gakets.

I had a question though. when doing the lower intake gaskets I know to put a bead of rtv along the front and rear of the block, some people say to put rtv around the water channels and others say not to. Any input on this would be appreciated.
Thanks

ASE doc

You have the 3.1 V6. Replacing intake gaskets on your engine is quite different from on a V8. To replace your intake gaskets you will need to remove all of the valve pushrods. Be sure to organize them so they dont get mixed up, they are 2 different lengths. Then clean the mating surfaces and as you were thinking, lightly surround the coolant passages with Permatex Ultra Black, both on the head and on the manifold base. Run the Ultra Black down to meet the end seals. Then run a thick bead of Permatex "The Right Stuff" along both end seals so that it touches the sealant around the coolant passages. Then lower the manifold base into position and install the bolts. Tighten the bolts in a circular pattern according to the service manual. If you dont have a manual, follow the guide that came with the gasket. Torque the manifold bolts to 18ftlbs. Then reinstall the push rods.

Having said all of this, if there is a manifold vacuum leak, it's probably in one of the plenum to base gaskets. The base gaskets rarely leak air. They do leak coolant and oil but not air. Carefully check all of the little hard vacuum lines these nylon lines like to get brittle and crack.

jakemussman

iTrader: (3)

Not good. I didnt take that into acount. The sucking noise is deffinitely coming from the intake area. I was going to pull the entire thing and replace all of the gaskets to be safe. I have the gaskets for a top end and throttle body rebuild. Maybe I will just do the middle intake, plenum, check the injector seals, and rebuild the throttle body. Removing the pushrods would really bump this up on the complications scale, and I have a limited time window as it is. Thanks for telling me that though. would have been much worse if I tore into it and found that out that way.

ASE doc

Yeah it sucks. Once you pull the base. You're stuck pulling pushrods. I've seen a few leaky plenum to base gaskets. Lots of oil and coolant leaks from base gaskets, never an air leak at a base gasket. Not on the V6s. Good luck. I hope it's the gasket. Or if not then a vacuum line under the plenum. Very common.