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'99 Saturn SL2 with symptoms similar to vapor lock

My '99 Saturn SL2 has from time to time in the past year or so had brief bouts where the engine will suddenly rev up to about 2000rpms while at a stop and/or drop down to about 650rpms combined with surging and stalling while moving. The Service Engine light would typically come on in conjunction with these spells, but then a few days later, things would be back to normal and the light would go off. The episodes seem to correspond with weather that has high humidity, but not necessarily extreme heat. Once or twice when the heat was above 90, the car quit completely and wouldn’t restart for several minutes, but that was last summer. About a month ago the car, which is normally parked in a garage, spent the whole weekend outside when we had some extreme rains (in air temps only about 60s or so). Since that weekend, the car is running frequently with the issues previously described, especially the surging and stalling while driving. It will feel like the timing of the fuel is all out of whack, will shudder and run hard, and then it will suddenly correct itself and run normally. A friend has a code reader and the codes that came up are 404 and 1404, which indicate the EGR valve. We replaced that with a new one and put in 4 new spark plugs, but the problem still persists. I believe the fuel pump is in the gas tank, so from other things I’ve read, a vapor lock may not be the problem since the fuel is being pushed. Could it need a new distributor or any other ideas?

If this started after rainy weather it might be the sparke plug wires, distributor cap, and or rotor (if it has those). Have they been replaced?

If the Service Engine Soon light came on and then turned off, the computer stored a history code. And with the proper scanner this history code can be retrieved to find out what caused the Service Engine Soon light to come on.

There are some parts stores that will pull codes from a vehicle for free. But the scanner they use must be able to pull history codes and not just codes when the light is on.

Tester

Neither P0404 nor P1404 mean that you need a new EGR valve.

P0404 is about the EGR circuit. P1404 for GM is that the EGR pintle is stuck open. This latter one could mean a problem with valve itself, although a good cleaning could clear it up.

But in your case with the P0404 in there, I’m going to guess that your EGR valve is getting juiced when it shouldn’t, thus opening the valve when it shouldn’t - and that fits perfectly well with your symptoms. Throw in the wet/humid weather and all you have is a wiring problem for you EGR. Now you track it down.

Surging like your car appears to be doing can be caused by a number of things, vacuum leaks, fuel pressure, O2 sensors, cat converter, EGR, PCV, IAC, engine computer, etc. Since your code shows the EGR circuit is failing, that’s the place to start. Until you get that code to disappear, there’s no point looking elsewhere. I don’t see this as a spark plug or distributor problem, at least that’s not the first place to look. I concur w/@cigroller.

Stalling can be caused by water getting on the high voltage components, but I’ve never heard of surging being caused by this. I’d be inclined to eliminate the high voltage circuits and wiring as the culprit. Surging is usually associated with a fuel/air mixture problem of some sort. Like a broken EGR system.

If your auto mechanic has one, ask him to check the exhaust gasses with his EG analyzer. That might provide a major clue that the problem is with the air/fuel mixturing.

Vapor lock was nothing like this. It was caused by heat boiling fuel in the fuel lines and forming vapor bubbles which prevented fuel from reaching the carb.

I go with the above. You have a false trigger on the egr . Possibly a vacuum issue, it depends on how your system is operated. The valve may just be sticky, these experience a lot of heat and depending on the design they can get carbon buildup. You cannot really “oil” this as it works on 900 degree exhaust. Dis-assembly and cleaning may work but given the age I expect at least part of the system is either leaking or rusted tight, so difficult to work on yourself.