Hot start rough idle, sometimes stall
 

Hi guys,

I have a recurring problem that I am at my wits end on...

Symptoms: hard start when hot, rough idle, sometimes a stall. Sometimes it will restart first try, other times takes a few cranks. Starts right up when cold, no stall.

Diagnostics performed: fuel pressure good, going to perform a fuel system leak down test to rule out leaking injector. Also, replaced fuel pump relay and problem persists. I have also searched for vaccum leaks and repaired the small ones I found. I have also cleaned TB and IAC valve. Plugs/wires replaced about 5k ago.

I have searched for possible solutions but everything seems to focus on CKPS. I don't think that's the issue (replaced sensor about a year ago, no stalling once running).

As far as how to proceed, I am thinking the issue is either (1) bad injector (leak down test will help); (2) IAC valve going out; (3) cam shaft position sensor; (4) coil going out; or (5) ??????.

I keep hoping an error code will pop up but I am not that lucky. Any ideas? Thanks in advance.

MAF issues would do this sometimes too. Too little air coming in at idle (i.e. at a stoplight) or too much from bad MAF will stall 'em out easily. When cold, not as much of an issue (my 01D2 did this same thing)

Clean it well with MAF cleaner and see if that helps. It's $8/can @ autozone, can't hurt to try.

Any O2 codes thrown? I replaced all four O2 sensors on mine and it fixed some similar issues.

Sounds like classic vapor lock, but not likely on an unmodified Rover. Make sure their is not some metal touching the fuel rail that could transfer heat from the manifold. I would also recheck the CKPS, a lot of things can happen to such a fragile sensor in a years time.


If you need some used parts, PM me. I have basically a complete engine that was in great shape (lots of new parts) except for massively cracked block. If you travel through Cahaba Heights, you can pick up at my store.

temp sensor can do this.
Put on a live scanner.
If the temp readings are way way off than that's it.

Crank sensor - if hot - and not totally failed may be giving out a skewed signal to the ECU.

Could be vacuum leak that comes on when the engine is hot.

You should have codes. Connect code scanner and look for pending codes.

Thanks for the suggestions. I don't have any codes (actual or pending) so I am hoping something becomes of the fuel system pressure test. If it doesn't I am going to have a ton more detective work to do. I just wanted to check with you guys to see if anyone had seen this issue directly. I can see where the MAF, O2 and fuel temp sensor would cause this.

I'll get some more data and report back. And Shade Tree, I may be in touch soon! Thanks!

You could pour a bottle of cold water on the CKP sensor to see if conditions suddenly get better.

Just wanted to follow up on the latest development. I took an old MAF sensor and cleaned it with sensor cleaner. Installed it in the truck and the RPMs are now solid as a rock at idle (650-675)! Thanks for all the help. I'm just surprised I never got a code...

The MAF is is a strange little beast. Mine is currently giving me fits while I wait on replacement part.

But yes, they can make your motor go ape$%*t and somehow throw no codes.

I liken it to not knowing you'll have to do a tough workout when you're eating chili for lunch....I'd stumble and sputter too if I didn't know how much fuel to put on board.

Glad you got it handled. Will tillery also sells used ones for $45, and new for $145 if you need one. willtillery@roverguy.com