1999 Pontiac Montana Two Problems

Tiny
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?
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Thursday, June 10th, 2010 AT 11:49 AM

6 Replies

Tiny
MMPRINCE4000
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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
Tiny
SFOX6173
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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
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Friday, June 11th, 2010 AT 9:58 AM
Tiny
MMPRINCE4000
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Coolant can only go two places, it is either leaking it or burning it.

Removing the intake manifold, you should always change gaskets.
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Saturday, June 12th, 2010 AT 8:23 AM
Tiny
SFOX6173
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Thanks again for responding. I do not seem to be losing coolant. The system just wont hold pressure.
The low coolant light comes on and off just because the level drops below the sensor in the radiator. It goes off when it fills back up. Just not steady pressure.

The engine issue has to be a sensor I believe. Just was hoping the you would know which one. I guess I will try the idle air control valve as it is one of the cheapest.

Thanks again for your thoughts
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Tuesday, June 15th, 2010 AT 11:39 AM
Tiny
MMPRINCE4000
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There is a coolant temp sensor that send temp info to PCM and a gauge sender that sends temp to gauge.

Hook up scanner to PCM in live data or freeze frame mode, when temp gauge goes high check PCM temp.

You could also have a bad waterpump.
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Friday, June 18th, 2010 AT 7:10 AM
Tiny
CLAY
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I have the same vehicle. Replaced several water pumps, head gaskets, intake gaskets. Still struggling>
Found new head gaskets leak some due to aluminum heads and tightening rocker arms after the head is seated. Try tightening the the rockers at the same time head is installed and letting it sit for a day to cure (use gasket cement).
Then you might want to run some an the Thermal gasket or other sealant in the colling system. To fill any small leaks.A compression test may surprise you to find leaking of cylinder gas into the cooling system thus pressurizing it with gas so the fluid is not operating properly.
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Wednesday, December 22nd, 2010 AT 4:48 PM

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