Hello,

I have a 1990 XJS V12 5.3L that idles a little rough at 700 rpm. If i press the gas pedal to about 900 rpm it smooths out a bit.

What kinds of things should I look at to smooth the idle. This is with 89 and/or 93 octane gas.

Thank you,

Mike Moore
1990 XJS Coupe
Tampa, Florida, USA

Submitted by zaphod_69@hotm… on Wed, 05/09/2007 - 18:07

Hi Mike

The HE engine never idled quite as smoothly as it's predecessor but it's normally not horribly bad ...the odd puff from one bank or other...If you are doing a great deal of short runs & gentle driving you could try a bottle of Injector cleaner & a good long run ..Hold it in selected Second & keep the revs around 3500 ..light load on the engine ..every now & then stomp on it for a second or 2 ( Get the full Load switch activated & the kickdown too ) sometimes it's just dirty injectors that aren't closing properly that mess up the idle.

Submitted by dwcurtiss@virt… on Tue, 01/02/2007 - 19:39

Hi Mike,

Just a few (gazillon) things might be causing the rough idle :o)

1. Spark plub wires might be broken-down(leaking)if they are older.
2. O2 sensors (two of 'em) might be suspect if they are older.
3. Spark plug gap - if too wide it will put a load on the distributor cap. If bad enough you could get a melt-down of the cap. (Good luck getting to plug #1; you'll have to loosen the AC compressor and move it out of the way).
4. Inspect the injection wiring harness for cracks; the wiring is subject to heat break-down since it is unfortunately located in the valley.

While you are at it - check the fuel injection lines for leaks - an ignition source + fuel leakage = engine fire.

Dwight Curtiss
2006 XJR
1990 XJ-S Conv