Need help!Engine stumbles/dies below 2000 RPM, unable to idle without keeping RPMs up

[Asudef]

It runs so rough that it has trouble keeping idle and stalls or very nearly so making it really difficult to move the car if at all. This is a 2001 2.0 LX FS-DE with 170k and never needed major service for anything, never threw a CEL or anything in it's life.

A little backstory:

The erratic idling started after a small service and 500mi drive which it did mostly fine.

I first had valve cover gasket, plugs, wires, oil and coolant replaced since it's had a slow leak (dark, wet, caked dirt/grease from valve cover seam). After that I did a ~80mi round trip drive and it was fine as well and then washed around the valve cover seal to look for potential new leaks with a spray bottle and bottle of water.

The next day I did the 500mi drive and now it'll stumble and feel like its misfiring when dropping below 2k rpms along with a tapping sound with quick jabs of accelerator.

During the drive I made 2 stops, first time it started up idling very low~(500) but mostly fine and I got back on the freeway. Next stop ~200 miles later was for a flat and started with horrible idle dropping the tach needle flat, dash lights flash and it'll pick itself up sometimes. Managed to keep the revs up and drove off slowly with no real issues. Limped it 50mi home @ 35mph with intermittent stops and it stayed alive.

Starts the next day and does the warm up rev fine at 2k and drops slowly to "normal" range. In D it sits at ~500 as opposed to the normal ~700 and feels rough like it could die any second.
The engine revs ok but with a bit of a tick like metal tapping on the valve cover and a "putt-ing" sound which goes away after driving a bit.

3rd time I managed to move it for parking by keeping the revs up in N and dropping it into D but anything past 1/5 throttle and it feels gutless but otherwise feels just like normal.

No dash lights at all, no CEL or anything. What seems to be the problem and where do I look?
Did the mechanic screw something up, did I get water where I shouldn't, is it just mileage/wear?

I had another mechanic look at it between 2nd and 3rd start and he thinks its the IAC or not getting spark. Parts store guy thinks its an alternator based on my description.

I think it might be all of the above or possible vacuum leak. Both 2nd and 3rd time starting was overnight so I'm thinking it may be a warm only issue. I'll try to get video if anyone thinks it'll help but I want to get this sorted within the week as it's still running on the dinky 12 yr old spare thats been used more than a few times. Right now I'm afraid to move it as it can die anywhere but I'm parked on the street.

 

[lolwut]

Lol, alternator? Really? It could be a number of things. No spark, stuck valve, fuel delivery problem, vacuum leak, the list goes on. You can check the spark plugs by simply pulling them out and holding them to the frame while cranking the engine. Youll be able to see if its sparking or not. You can check for vacuum leaks by taking brake cleaner and spraying around any and all places air could leak/get in and listening for a change in engine sound or performance. You should probably do that while the engine is cold so that youre not spraying combustible s*** on a hot engine. Test fuel injector harnesses, Crank Position Sensor, Cam Position Sensor, Idle/Throttle Control Sensors with a multimeter. Check the EGR, and PCV valves. Good luck.

 

[MaxPower]

Most likely you have 1) a vacuum leak or 2) a stuck EGR valve:

1) a) Start by inspecting the ENTIRE accordion tube from the airbox to the throttle body. This probably has a giant crack in it somewhere. You should remove it from the car to inspect it because there are often cracks invisible from above. If this needs replacement, you can buy it shipped to your door for $35 and can tape the current tube up until it arrives.

b) Also you need to make sure every vacuum port near the throttle body has a hose attached.


2) The EGR usually causes an intermittent rough idle depending on when it's stuck. To inspect it, you would have to remove it from the car. It's not too difficult, but does require the right technique and right tool. You can find a walkthrough somewhere on here.

Post up your results.

 

[thuzil]

^Vac leak

Easy way to test this is to get a coupler that fits over the maf, get an ABS pipe cap that fits in the coupler. Drill a hole in the pipe cap and fit with a compressor fitting. Remove your intake system before the maf and hook the coupler to the front side of the maf. Clamp everything up and pressurize your intake system to about 4 psi. Listen for hissing of escaping air and repair any leaks.