My cat has recently started idling a bit rough. It will crank fine and then drop to around 5-600 rpm where it shakes noticeably and sounds as if it will stall out.. then it will recover and rev up a bit to around 900-1100 rpm.. then it will drop down again but now idling a bit better.. then back up and after about a minute or two it settles into a nice idle around 900 rpm. I've attached a video. It is worse on first cold start. After the car is driven or up to temp it still may not idle great on first start, but not as bad. I've looked for the typical suspects.. any input is appreciated!

 

VIDEO on youtube because this forum does not appear to accept either video mp4 or mov files:

 

I suspect you have a vacuum leak. Unmetered air is finding its way in and the ECU doesn’t know what to do. Check for leaks somewhere between, and including the MAF and the Intake Manifold.

It could also be your Idle Air Control Valve, failing Coolant Temp Sensor or a malfunctioning or dirty MAF.

I would also ask you when you last cleaned your throttle body.

What happens when the car has warmed up?

 

Everything Vee said plus look at the MAF connector. They sit awkwardly and sometimes. After all the self evident items, take a look at the ECU pins and make sure it hasn’t suffered from water ingress. I would do that last, after you have checked under the bonnet properly though

 

Good point Spikepaga,

Sometimes, the connector to the MAF gets crunchy. While the engine is running, if you wiggle that connector, without disconnecting it, and get the engine to respond, then we need to take close look at that connector.

Sometimes you need to replace it, sometimes you just twist the pins so they make better contact.

 

Thanks for all the help. So I removed the TPS boot and cleaned the throttle body good. I don't think it had ever been cleaned and indeed had some buildup. I started and drove it and then cranked it again a few times and of course the car is warm now so it is different, but it will crank and idle about 600 rpm for about 30 seconds before raising to 900 rpm and settling there. I'll have to give it a cold start in the morning to see how she does.

The MAF connector is solid and I wiggled it with engine running and it made no difference. How do I remove the MAF? Where is the Idle Air Control Valve and what do you recommend there?

 

https://www.jaguarforums.com/forum/x...diagram-45150/

The screws holding the IACV in place have loctite, so beware removing them, you may snap these small bolts. I would recommend replacement.

Removal of the MAF should be obvious. I believe hose clamps keep it in place. You’d have to spray some MAF cleaner spray through the mesh that protects/filters the incoming air.

 

I’ve got a new set of plugs I’ll put in this week and see if that helps things. I was told by a Jag mechanic that plugs should be changed every 30k miles in these cars, and she’s at 52k right now. That sound about right?

On another note does anyone know where I can get a new flywheel for the 4.0 car? I’ve seen used but prefer new if possible, but all I find online are expensive Fidanza aluminum ones for $400 for the V12 models. They’re even a cool green and all which almost makes me want to spring for it. Is the flywheel the same on 4.0 and V12 engines in 1996?

I did find this one but there's no pic and from the details provided I'm not sure if it's what I need or not.. thoughts welcome:
https://mossmotors.com/flexplate-2?assoc=119353

Thanks to all

 

If the flywheel is part of the transmission, then no. It will not be the same for a 4.0

Plugs should indeed have been changed by now. They don’t last long, but they are cheap and easy to replace. Don’t make the mistake of buying longer lasting plugs, like iridium or platinum plugs. The cheap copper/nickel ones are the ones that work best in these cars.

 

Bigcatrescue - Just curious as to why you need a new flywheel. I have a 1996 4.0 and I was sure that I had a broken tooth on it or the starter because it sounded like it would jump a tooth when I started the car. The car was also intermittently stalling. Guess what? Both problems cleared when I installed a new cps.

 

The flywheel issue is one I have written another post about and has plagued me since I bought the car last year. I replaced the starter to no avail. The culprit is no doubt a small burr on the flywheel that makes a somewhat grinding spinning sound briefly on some starts.. depending on the position of the burr. So I can either remove the starter and try to find the burr and file it down.. or replace the flywheel altogether. Car runs and starts fine it's just an embarrassing noise that I'd rather not live with.

 

Are you sure it’s not the chain tensioner, or the harmonic balancer? Both are known makers of startup noise. The first one causes a rattle at startup; the other a squeal.

 

LOL one thing at a time please. I have a rattle, but that's coming from the exhaust somewhere near the middle of the car. That's lower priority. I have a squeal too, but that's coming from new belts I had put on and although they said they were tight I'm going to have them check it again tomorrow when I put new brakes on it.

Back to the grinding noise.. 95% sure it's a burr on the flywheel.. which explains why it is intermittent depending on position of it during startup. It's certainly a distinctive sound.

Other than the rattle, squeal, grinding and rough idle she runs great

I just realized if you watch the video I posted above you can hear the belt squeal and grinding noise on startup. Note these are 2 distinct issues and sounds they just happen to be heard during startup. The belt squeals only occur when they are not up to temp.