Hello all, I just switched out the Jarvik heart thermostat for an inline thermostat and it greatly improved temps. However, today the disco developed a slightly rough idle. Seems to smooth out when on the gas, but returns to a rough idle or misfire when idling. Does that generally seem like a fuel blockage issue or misfire due to spark plugs/wires? Any suggestions on the first place to start checking?

 

Is the SES light on or flashing? If so, have you had the diagnostic codes read?

 

Maybe running a bit too cool now?

 

No SES light on. Prior to the inline thermostat swap, I put in a new regular thermostat and temps would fluctuate between 208-216 with going easy on the throttle. Now with the inline thermostat it's running 175-185. It has a feel like a slight fuel clog since it seems to clear up when on the throttle. But not sure. Sounds like the fuel filter is built into the fuel pump in the tank, so would rather make sure that's the issue before digging into that.

I was just reading on the site about the idle air control valve as a possible cause for rough idle. Thought about removing that and cleaning, but not sure where it's located. Found a video for location on the 4.0L in the D1's but don't know where it's at on the 4.6L.

 

 

Mine idled fine, but would die if you gave it even the slightest throttle input. It was the idle air control valve. I was going to replace it, then read a post here by Best4X4 (I think) saying he had never seen a bad one. So I cleaned it good with carb cleaner and that did the trick. So, don't replace it until you have at least given cleaning a shot.

 

I did take the idle air control valve off last night and shot a fair amount of brake cleaner through it. The throttle body looked clean. Pulled a few plugs and they looked ok, but got another set and will replace anyway. I ended up dumping injector cleaner in the tank since it's 1/4 full and let it chew on a concentrated formula. Seems to be idling better this morning. I have a feeling some injectors are getting a little clogged. I'll run this tank down a little more, then add another injector cleaner bottle at fill up. I think it's coming around.

 

What spark plugs did you buy? Double platinums, I hope (e.g. Champion 7070s).

 

Bosch R6 double platinum

 

I have an 03 with 180’ inline thermostat mod. It’s had an off and on slightly rough idle and occasionally a P030x code (random misfire).
Was doing this long before changing the thermostat.
Coils are good.
Have cleaned the IACV.
Plugs and wires have about 60K miles on them. Being doing this for ages.
No vacuum leaks, have had three different shops look and try to find what’s up and no luck.
Nothing seems to sorted out.
I usually clear the code(s) and ignore it.

Was getting a failed steering pump replaced recently, the shop pointed out that spark plug wires on the driver’s side where touching each other and starting to show slight white discoloration on them. Mechanic recommended that I spend a few bucks on spark plug wire holders. I did that, and tidied up the spark plug wire routing. Since then no rough idle and my MPGs have gone up. I do believe the steering pump was going bad for a long time before it failed (broken shaft) and that’s more likely the cause for MPG change.

Anyways, maybe check your spark plug wire routing and make sure the wires are spaced from each other. Next time I do wires and plugs thinking of relocating the coils on mine.

The passenger side on mine had wire spacers. So I’m thinking on the driver’s side the spacer(s) fell off at some point or where never installed (I had a Turner engine swapped in when I bought the D2).