My daughters 2002 Saturn SC2 is having an issue. Acceleration is no problem at any speeds, but once I settle at any speed below say 50 it chugs a little. It's like it's stalling for a split second every second or so.

I brought it to a mechanic and he put it through tests. He couldn't identify the cause but says the symptom is that it's running very rich. So I'm assuming what's happening at low cruising speeds is that it's flooding out.

I googled and found several people with the same issue solve it by replacing the EGR valve. Well, $140 later and a new EGR valve I still have the same problem. The mechanic didn't think that would be it but since he had no other idea I replaced it.

Also, 75% of the time if you come to a complete stop with the A/C running it will die. My daughter has developed the habit of sliding it to neutral at red lights.

On the highway at 70+ it doesn't miss a beat. Runs great.

Anyone have an idea of what to attack next?

A bit of history... She ran it out of oil last year and wore a main bearing out, smashing a piston, bending a rod and wearing the crankshaft so much it had to be replaced. I rebuilt the engine, replacing the crankshaft, rod, and piston. (and all bearing of course).

I only mention all that because while I'm not totally lost around an engine, I am not a pro, IT Tech by profession. I may have made some blunder deep inside that the mechanic didn't even think about because in normal wear would not happen.

I welcome your input!

 

Something else the mechanic thought might be it is that I got the timing chain one link off. Any merit to that?

 

I'm betting on the engine coolant temperature sensor (ECTS). Replace it along with it's associated connector. Use OEM parts from nearest Saturn friendly GM dealership. Parts will cost about $40 usd. Make sure the new sensor has the metal tip, and not a resin-coated tip

 

Have you had the engine codes run on it? If not, try that and post the codes. Running rich could have screwed up your O2 sensor.

 

Replaced the ECTS per OceanArcher's suggestion. The old one looked in rough condition but it did not improve the performance.

Stopped at a parts store and ran the engine codes got these:

P0107 (Mass Air Flow sensor condition)
P0108 (Mass Air Flow sensor condition)
P0122 (Throttle Position Sensor)
P0172 (Fuel trim bank one condition)

I forgot to mention earlier, the mechanic DID replace the O2 sensor in his attempt.

I said that it seems to chug for a split second every second or so. Actually it happens much faster than every second at low cruising speeds of 30 or so. I took it out on the highway and I can still feel it at high speeds, but very subtle. I think it's just harder to feel at high speed.

Something else new to add: In park idling with no a/c or the a/c on low is ok, but if I crank the A/C to high it'll sputter and eventually die. Could that point to electrical?

 

Try tapping on the MAF while it's running. If it stumbles, then you've found the most likely problem. I'm not sure, but I think you can remove the TPS and clean it. Check all of your electrical connections for corrosion. It's a real pain in the butt and can cause all kinds of problems.

 

Where did you buy the ETCS and did you replace the connector and how was the connector attached?

 

Got the ETCS from o'reilly autoparts, the cable was a tiny two pin that then went into the wiring harness. It was located under the EGR valve.

 

You ignored the first bit of advice.

I'm betting on the engine coolant temperature sensor (ECTS). Replace it along with it's associated connector. Use OEM parts from nearest Saturn friendly GM dealership. Parts will cost about $40 usd. Make sure the new sensor has the metal tip, and not a resin-coated tip

Take a look
https://www.saturnforum.com/forum/general-tech-help-13/etcs-its-connnector-6417/

Replace the ETCS
Replace the ETCS Connector
Buy both from the dealer.