94 Olds 3800 cold stall check engine

My 94 Olds 88 / 3800 (127k miles) has started to stall and surge when starting on cold mornings and check engine light comes on. Low coolant light also has been coming on occasionally over the last few months, but not at
morning startup. Took it to a repair shop, told them my story and they checked it out. Said crank position and low coolant codes came up and that coolant is leaking into intake and on some sensor below throttle body causing the codes. They say it needs a new throttle body / intake kit to the tune of $250 plus $250 labor. All fluids levels are ok and clean, none have dropped noticeably. It idles fine and has plenty of power when warm. Haven't pulled the plugs but I just don't agree with this diagnosis and mechanic will not guarantee this $500 fix will cure problem. I thought it was an O2 sensor, but they say no. Any ideas?
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Engine could very well have coolant leaks, I also have a 94 olds 88 with same engine and 150,000km, it recently needed about 1000 canadian dollars worth of coolant leak repair, one of which was an engine gasket (not the head gasket but i cant remember exactly which other one), another was some plastic coolant fitting that was prone to breakage and was ready to blow up at any second that had been obsoleted by an improved metal part. Earlier on I had a problem with stalling at random times be it at parking lot speeds or highway speeds(it happened at 80km/h, scary). No computer codes at all, took it to a shop and 2 dealers and they could find nothing, then when I had it emissions tested (here in ontario we have this program called drive clean where you have to get your tailpipe gases analysed and your car fixed if things are out of acceptable limits) it failed the test and the guys immediately knew it was the O2 sensor just by the readings, they replaced it and poof stalling problem gone. The kicker was that the dealer and shop id gone to before didnt check the O2 sensor because i told them i had only replaced it 5 months or so ago( i had done a tunetup with new platinum plugs, wires, o2 sensor) and the O2 sensor had failed prematurely. The dealer is not always right. Just some food for thought for you. It is a great car otherwise (as im sure you know :) ) and has been relatively bulletproof mechanically.
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Thanks for the reply. Where is the O2 sensor on this baby? The mechanic may be right but before I dump $500+ into it, I'm going to replace it just for kicks.I'm also pulling the plugs this weekend, if it's burning antifreeze, there should be some signs...

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The O2 sensor is pretty easy to get at, although i found it was easier to change from underneath the car. Look down at the engine at the back side near the firewall in the middle where the exhaust manifold comes out to meet the exhaust pipe going to the catalytic converter. The sensor is in plain view and looks like a bolt screwed into the manifold with 2 wires sticking out of it and a connector after maybe 4-5 or so inches of wire. Just use a wrench and it unscrews straight out. I suggest you disconnect the wiring connector first as it is stubborn and even tougher to disconnect when the sensor is dangling in midair. Be careful when changing it as apparently the O2 sensor hates being bumped around or dropped. I think thats what may have caused mine to fail so soon, as I vaguely recall dropping it a few inches when taking it out of the box. My old one had yellowish brown crud all over it, probably sulfur from the exhaust or something. Good luck and let me know how it goes!

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If an engine is burning antifreeze it can screw up the O2 sensor. Seen it lots of times customer replaces leaky head gasket and brings it saying it still runs crappy and fouls up plugs! What had happened is all the coolant they were burning had damaged the O2 adding to their problems.
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The throttle body has a blue neoprane gasket that seals the throtle body and engine coolant to the intake manifold. It needs to be replaced because it is leaking onto the engine coolant sensor under the throttle body. You can pick up a new gasket and change it in about two hours. Remove the three nuts and a small braket attached under it. Good luck
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I did the O2 sensor and plugs today, both were fairly clean and new parts didn't help the issue. This gasket change sounds easy, but any possibility the throttle body bolts just loosened up and could be tightened down? The mechanic's fix was a $250 "gasket kit" (plus labor) - they were vague as to what was actually being replaced.

and engine coolant to the intake manifold. It needs to be replaced because it is leaking onto the engine coolant sensor under the throttle body. You can pick up a new gasket and change it in about two hours. Remove the three nuts and a small braket attached under it. Good luck

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Got the blue gasket today. I was expecting a head gasket look with round passages, but this has wide open areas and is thick like the valve cover gaskets. Think it's worth changing that sending unit that's being leaked on under the TB while the TB is off?

and engine coolant to the intake manifold. It needs to be replaced because it is leaking onto the engine coolant sensor under the throttle body. You can pick up a new gasket and change it in about two hours. Remove the three nuts and a small braket attached under it. Good luck

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