1999 Pontiac Montana Two Problems

SFOX6173

MEMBER
1999 PONTIAC MONTANA

Engine Cooling problem
1999 Pontiac Montana 6 cyl Front Wheel Drive Automatic

Had upper and lower intake gaskets and head gasket replaced by a shady mechanic. He seemed to get my coolant to stop leaking. Worth $1000? Not too sure.
Can not go back to see him anymore. Trying to avoid jail. Can not sue him. Dont think he is legal. Oh well. Trying to fix issues myself as I am out of money. Thus, driving a 99 van.

Had to pull upper intake back off to replace a bad coolant temp sensor wire. Did not replace gaskets as they were brand new and looked fine. Now, can not get coolant system to hold pressure. Have installed 2 thermostats, temp senor w/ wire, and a water pump.
Tried to bleed the system several times. No luck. Coolant not leaking from anywhere. Heat is hot. Fans work as they should. Still overheating at a stop. Low coolant light comes on every few minutes. Any ideas?

Next, Engine starts and idles normal. Push the gas peddle while driving and RPMs go very high and speed does not respond as it should. Sometimes pedal goes dead as if the engine was turned off. When RPMs drop down below 1000 it will pick back up and go. Also getting a bucking throughout the drive range. Repair manual says check emissions vaccuum leaks and wiring. Hoping to narrow it down a little. Throttle postion sensor is new. Removed idle air control valve and cleaned it. Very dirty. Unpluggd mass air and it runs worse. All wires have proper voltages. Connections are hard to check but all pins look good. Going to try to clean EGR today. Cleaned throttle body already. Replaced computer as well. Any thoughts?

6 Replies

MMPRINCE4000

MECHANIC
8,548 POSTS

The overheating may simply be a bad temp sender, unless it is gushing steam?

Second problem may be more serious, start by checking trans. Fluid level.

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Friday, June 11th, 2010 AT 7:59 AM

SFOX6173

MEMBER
3 POSTS

Thank you for your thoughts. This issue is not the cause of the transmission. It is from the emission systems. EGR, Mass Air Flow Sensor, Throttle Positioning Sensor, Idle Air Contol Valve, Map Sensor. Not the trans. Could be wires to one of them. Could be connections. Could be computer. Not trans. Was hoping for someone to know just the issue or that could reccomend the first thing to try.

Cooling system issue is also not comming from temp sensor. It is new as is the wire that connects it. Was not having this problem after it left the shop. System is not leaking coolant but not holding pressure. Low coolant light come on and off because the level is falling in he radiator. Sensor is reading high temps on the dash. Temp drops as car is moving only overheats while sitting at idle. Fans are working as they should which I believe to be another sign that temp sensor and computer are working. Just wont hold pressure. Heater blows hot so not a heater core issue. Water pump is new. Replaced two Fail Safe thermostats by Motorad 195 temp rated ones. Both thermostats were stuck open. A clear indicication that the van is overheating. Just wondering is the system is sucking air through the upper intake that I removed. Could this happen without coolant leaking out? As I mentioned, I did not replace the gaskets as they were brand new and looked good. Lastly, I will be more than happy to make a donation if this site helps me solve my issues. Bad temp sensor or transmission are not the solutions