I've been battling a rough idle and no-start issue that's sporadic and has some pretty odd symptoms. I thought the rough idle might be a dirty IACV, so I took it off yesterday and sure enough, was pretty gunky. I cleaned it all out and spins freely in-hand.

So today we went on a Costco run with it and it ran super smooth on the way there. I thought the IACV must've been it then.

After we loaded up the groceries and started it, it began to run pretty rough like it used to. Drove it the quick jaunt to Costco gas station, filled it up, and then went to start and it just straight up wouldn't.

Cranked and cranked, and it just wouldn't catch. I had recently replaced the coil packs so maybe those were bad? I swapped them out with some spares I had in the back but that wasn't it. Finally I went to try again and after a couple more cranks, it finally choked to life and we hobbled home.

We had to take some neighborhood streets and had to nearly run every stop sign (safely of course) because when it's at a stop, that's when it wants to choke and die.

I recently replaced the O2 sensors (upstream) and have no reason to suspect those. No related codes and all was running fine a couple weeks ago after replacing them. But then again... that's the most recent change so obviously can't rule it out. I reset the adaptive values btw.

I tested the (original, 205K) fuel pump last week and it was reading normal during a cold start. Do fuel pumps go bad in a binary pass/fail way or can they do something like this as they make their way out?

Here's a video of it when we got home. REAL rough idle O2 sensors seem to be working fine:

 

Also should mention that the CPS is original, but my understanding of it failing is that it either works fine, or it kills the car. Not like a degradation issue that I'm experiencing.

And battery is new and fully charged (checked it yesterday).

 

CPS do go bad gradually. It is a heat related issue. Often manifest as starting fine when cold but not starting when hot. You can pour a glass of water down the drivers side rear of the engine and if it is a bad cps it will cool off immediately and start. You can either install an aluminum heat shield or wrap the factory cover in aluminum foil and it may cure it. As far as the other troubleshooting, if you unplug iacv, maf, and oxygen sensors the engine starts using only basic inputs like throttle position and rpm for fueling and spark timing. If the 02s are cycling, you can leave them plugged in. I often unplug the maf and iacv to test them often as the first thing.

 

I ordered a new fuel pump, thinking whether it's bad or good, it's 205K miles old and might be worth it just to preventatively replace. A new Bosch unit from Rock Auto was only $150, which is hardly worth thinking twice about given this and our L322 are our daily drivers.

I'll throw in a new CPS too. Similarly thinking... even if it's not bad, it *is* old and I'd rather put a new one in with the comfort of my shop rather than on the side of the road someday. When I changed out my head gaskets, I left the connector free of its little retaining clip to hopefully make changing easier.

 

When the CPS gets hot it will fail to start classic symptom. Usually if you wait 20-30min it'll fire right up once it cools down or if you pour water over it. Whatever you do DO NOT get a generic CPS. Go with Bosch only. The aftermarket ones might last 2-3 months before they die!

 

Reporting back. Just as a control test, I attempted to start this morning and it cranked but no start still. Another tick mark in the not-the-CPS column.

Nevertheless, I never felt great about driving around with the OG CPS, so installed a new Bosch one anyway. Sidenote... really easy job made easy only by the forethought I had *not* to clip the harness side of the connector back into the holder when I had the engine torn apart for the head gasket replacement. Connector was easy to take apart, quick to install, left on the ground and didn't take the exhaust off. Even got my little torque wrench in there to tighten down the bolts. I was prepped for a nightmare with the way most describe the procedure. Was pleasantly surprised. Anyway... still no start, but at least can stop being paranoid about a roadside issue.

Swapped in a spare MAF I had, no start.

Tomorrow the fuel pump arrives so will report back once that's installed.

So far we got...

Air: Not the MAF, not the IACV, still haven't checked the throttle position sensor but seems unlikely without a code.
Spark: New wires, plugs and coil packs. New battery and it's been hooked up to a trickle charger this whole time and is at 100%.
Fuel: Likely fuel pump? Injectors are most likely not the issue if I'm not getting a misfire code on one specific cylinder. Also I replaced all the o-rings on those when I replaced the head gasket a few years ago.

 

Might still be the IACV if something is wrong with it and makes it stay closed. Does the car start if you press the pedal a little while starting?

 

You can have the MAF unplugged it'll stumble to start but it will eventually run as the ECU goes to a default reading. If it was fuel you should be able to spray something in the intake and it should at least cough vs absolutely nothing.

 

Unfortunately no, but good thought I didn’t really consider.

 

Clarify that second part if you could? I’m not tracking.