Can an exhaust leak cause poor idle

I smell it while driving only with the window down. I lose a little coolant every let’s say 60 miles. I have poured UV dye into the tank and have driven 100 miles but nothing glowing green pops out at me under a black light, I did find some spots of suspicion on the left front bumper/fender, I need to pull the trim off to get a better look but the rubber boots that hold the screws have rotted/ripped. But from my understanding my 1991 doesn’t have anything that could leak coolant in the area compared to earlier models that have the overflow tank in the left fender well.

The engine oil and coolant do have a similar sweet/odd smell that makes me think it to be a strong indication of head gasket failure. But no visual signs of mixing. Losing coolant with no signs of external leak. And I can’t stand the smell while driving with window down. Now my car does leak a little oil and power steering fluid which MIGHT explain the smell while driving but doesn’t explain the loss of coolant. Car drives perfectly fine though and gets to 90mph easily. Also my expansion tank stays pressurized after driving for at least a week, I hear the pshhh shhh air bubbles and pressure escaping sound when opening the expansion tank cap

Actually they were clean, it turned out to be the heater core barrs leak solved the problem! Apparently it is recommended to add at every cooling system flush

Might be the heater core, you wouldn’t see the leak dye in there.

That used to be truebut Jaguar removed it from the XJ40 service schedule some years ago after apparently some nasty clogged radiator cores.

I too have used Barrs Leak successfully once only in an emergency on the Jag and other cars with miraculous effect and no problems downstream

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I was tempted once, even bought some but decided to find the leak and fix it instead.

Unfortunately mine was in the heater core, I really didn’t want to go there.

Fair enough, still managing to keep away from that job!

Just tried setting the iacv per the above link, sadly with the valve fully closed I can’t get below 750 rpm, any thoughts?

750’s ok in park, what’s it in drive? 600-ish? or is it 750 in drive?

600ish in drive, I was just curious if my stepper motor is really seating as I can close the valve hard and still only get 750 rpm, I did crack the vve to let some air in.

One more thing, I can hear the stepper motor “clicking” for awhile.

Well those revs are ok, but if you want you can get a new stepper motor, cheap like borscht if you don’t get the jag one. I’ve been running a renault magane one for about 8 years even though I probably replaced the original one unnecessarily, my own rough idle issues back then turned out to be vacuum related not a failing component.