Butterfly adjustable?

In diagnosing my current high idle I've noticed that a lot of air is getting past the butterfly at idle; there is major suction when I hold my hand on top of the main throttle body port. How do I go about adjusting the butterfly to close tight?



BTW...my idle is getting better, after adjusting the Auto Tranny cable plunger / throttle my idle after warm up/driving is down from 1500RPMs to 1100RPMs. I'd reccommed anyone else with issues fiddling with the TB to check this.

If the butterfly adjustment and a second TB cleaning doesn't bring it down another 1-200RPMS I will have to think about a new TPS . My input voltage is 6.5v and 82% of that just aint cutting it. I'm a little confused about this part of it all; the FSM doesn't say anything about too high or too low an input voltage at the TPS, just that the output needs to be 82-83% of the input. I've asked before about this and no one seems to know.

Dealer wants $166CDN for a TPS. I can get one for $105CDN a half hour away in Montana. I can't seem to find a source on-line for the pre90 I6.

Somebody should write a book on idle issues.

There is an allen-type butterfly adjusting screw for the idle speed, but only alter this as a last resort! You must be certain your problem isn't TPS - related, or some other external cause. Also check for vacuum leaks.
Its been a while since I had to buy a TPS, but I got the last one from NAPA for around $75.00 CDN.

I would go ahead and adjust the throttle plate stop screw to minimize the air leaking past it. I backed mine off until it wasn't acting as a stop and then turned it back so that it very-very slightly started to move the throttle plate. In my experience, the TPS doesn't do much to the idle speed but there are others who believe otherwise. You can play with sensor and decide for yourself. You didn't mention whether or not you tried to adjust the TPS but you should do so if you haven't already. If you need a new one, rockauto.com is a good source.

There is also a small round idle air passage that comes up through the top of the throttle body on the right. That could contribute to your problem if it is misadjusted.

What are these "problems" that you can have if you adjust the throttle butterfly anyways? I heard it just masks Idle issues and creates more problems later.

Dave - What year XJ is your XJ because my local Napa in Canada can't find one for my '90 I6 (the USA Napa could!). I ended up getting one online via Checker for $100CDN with shipping.

Paul - As I noted my TPS readings are way off (input is at 6.5v) and when I adjust it to 82-83% as the FSM suggests it causes a 2500RPM idle. I haven't touched the idle air passage hole you mentioned (not the IAC right?) but will look for, thanks!

I figure a new TPS can't hurt with the readings the current one is giving, but I don't see any way around adjusting the butterfly...it's not closing fully and nothing else besides the adjustment screw can correct it.

Thanks for the replies. Can anyone explain my high input reading???

Can't help you with your high TPS voltage reading, but I recently had a little trouble with my XJ revving to 2500 rpm on start up as well. My idle had been running a little on the low side at 650 rpm.

I checked for vacuum leaks, made sure the intake manifold bolts were tight, these were all good. Next I cleaned the contacts on the TPS, AIC and cleaned the TB and linkage really good. Still had a 650 rpm idle, with ocassional high revs at start up.

Just for the heck of it I checked my air cleaner. When further inspecting it, I noticed one side of the filter was seated incorrectly. The filter was a little on the dirty side as well. The filter houseing on the 10" length side of the filter had bowed out a little, causing blow by past the filters edge. Possibly disturbing the vacumm in the filter box? Not to mention crap going into my motor. At any rate I replaced the filter and made sure to seat everything correctly.

What an improvement. I'm now idleing at 750 rpm's smoothly, with better throttle response and no high rev's at start up.

Just thought I would share my little experience. Theres always something going on with an XJ's TPS

LynchMob said:

Dave - What year XJ is your XJ because my local Napa in Canada can't find one for my '90 I6 (the USA Napa could!). I ended up getting one online via Checker for $100CDN with shipping.

Paul - As I noted my TPS readings are way off (input is at 6.5v) and when I adjust it to 82-83% as the FSM suggests it causes a 2500RPM idle. I haven't touched the idle air passage hole you mentioned (not the IAC right?) but will look for, thanks!

I figure a new TPS can't hurt with the readings the current one is giving, but I don't see any way around adjusting the butterfly...it's not closing fully and nothing else besides the adjustment screw can correct it.

Thanks for the replies. Can anyone explain my high input reading???

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Adjust butterfly only after ya have done EVERYTHING else.

Check this, might help some:Basic Sensors Diagnostics might help ya. (Renix based page.) Also some info on Downloads page.

Poor ground connection from TPS connector to 'ground'. Check the voltage leakage on the ground wire - I'm guessing there's > .1v on the ground. If you'll add a jumper wire from the connector pin to the firewall ground you may see the voltages more accurately. (Solved one of my idle issues.)

While you're at it, ADD an additional ground cable (4/0 ga. or better) from the battery to engine ground point then around the engine to the existing head to firewall ground. OEM depends on ground to travel through engine & a puny firewall strap ground on the back of the head. (Not a suspected cause of hi-idle problems but I've seen it cause some crazy things when that crappy ground strap dies/oxidizes.)

Just a couple things to check.

I agree, do not adjust the stop for the throttle until you have done everything else.

I had a 1500 rpm idle until the dealer mechanic adjusted the stop BUT he had first hooked up the test set to make sure EVERYTHING was working right. He did this adjustment AFTER he cleaned the throttle body. You could have a sticky Idle air controller which is letting in too much air, that why you have the high idle.

It might be worth is to take it to a mechanic with the test set and understands the renix 4.0. Go in with "Idle's too high" and have him figure it out, the last thing you want to do is adjust the stop if it something like a dirty idle air controller, a dirty throttle body, a bad sensor, etc. It might be worth an hour of dealer time. I also stood there with the tech as he checked over my XJ. My tech does not care if I stand there or not. We chat and I ask him stuff, he asks me stuff also.

Lunghd's suggestion about the ground wire to the TPS is very good. If the original ground is poor, splice in another wire and ground it to an engine bolt.

If you must adjust the throttle stop screw, first disconnect the ISC. Then adjust the screw to obtain a VERY slow idle; barely above a stall. Then plug the ISC back in. This allows the ISC to regulate the idle speed. The throttle body should be clean before you attempt any adjustment.

As others have said, do the screw adjustment as a last resort. There's nothing to get it out of adjustment from the factory, unless someone has fiddled with it previously.

Thanks for the suggestions and info thus far guys. Here's a little update on where I'm at with this, maybe with the additional info someone can pin point a problem.

After a good TB cleaning and installing a new IAC the idle on start up seems right. At startup it goes immediately to 1500rpm then drops to a steady 600-700rpm (was lingering around 1000rpm). After driving for several minutes, in Park or Neutral it still idles between 1200 and 1500rpm depending on the temperature outside (the colder the higher...but no more than 1500rpm). If I let it sit for 10-15min it will eventually go to normal base idle. Sound familiar in anyway?

TPS is ordered and I should get it in next day or so. Mine has a good ground but screwy input and output readings that won't adjust to spec). I like to hope this will fix it but I'm doubtful.

I'm going to go with consensus and not mess with the adjustment screw, just yet, but still think my butterfly is open too wide...CAN ANYONE tell me what a normal position for the thing to be is? Mine doesn't sit flat and a lot of air is getting past it...this is with the stop screw is making contact.

Also on list is tightening the valve cover and intake manifold bolts. Any other suggestions?

LynchMob said:

CAN ANYONE tell me what a normal position for the thing to be is? Mine doesn't sit flat and a lot of air is getting past it...this is with the stop screw is making contact.

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It's kind of hard to say, because all of the throttle bodies I've seen had at least a little wear on them, but it appears that the butterfly should be almost, but not quite, resting on the bore of the TB. You don't want it to make enough contact to wear or to stick. What I did with my 87 (which had already been messed with) was to slip a piece of paper between the lower edge of the butterfly and the throttle body, then adjust for a little drag on the paper. It has idled well for many many miles and some years, so I conclude that I at least did no harm.

Adjust it like Matthew says. Worst case, you can put it back the way it was. It's certainly not an adjustment that is non-reversable. You can pay attention to how many revolutions or quarter revolutions that you readjust it and easily get back to the current setting. There should not be a lot of air getting past the throttle plate at idle.

Almost fixed I know it!

I'm still having idle issues. So far I have:

Replaced PCV grommet, vacuum hoses (Mopar 2pk kit), IAC and TPS (with added groundl).

Cleaned the TB, Air filter, installed new Return Spring (& added dual backup spring)

Torqued Valve cover and propane tested TB and Intake Gasket.

My high idle AFTER driving and shifting into Neutral or Park is still occuring. If I wait approximately five minutes the idle comes down to a steady 800rpm.

My base idle at start up seems fine...this makes me wonder whether an adjustment to the butterfly would do any good.

Any tips on checking vacuum hoses? I can't think of any other cause.

FYI: the new TPS readings are about the same as the old one: 6.8V input, 5.54V output, 0.02V ground. The only difference I notice is at start up the idle shoots to 2000rpm and then comes back to about 750rpm (before it would only shoot to about 1500rpm) and that there's a smoother acceleration and deceleration.

My '90 has some of the listed idle problems on an intermittent basis. At start up it will jump right up to 2000 RPM and then settle back down under 1000. Sometimes it will keep the high idle and after a few shut-off/start-up cycles, it will return to normal. Something I have considered is that a leaky injector might have something to do with this. If the injector drips after shutdown, then there would be some raw gas puddled in the intake runner or intake port that could cause high idel at start-up. A consistently leaky injector might cause a high idle until the engine warmed up enough for thermo expansion of the injector body forced the leak closed.

Just some more thoughts to mull over.

MaXJohnson said:

My '90 has some of the listed idle problems on an intermittent basis. At start up it will jump right up to 2000 RPM and then settle back down under 1000. Sometimes it will keep the high idle and after a few shut-off/start-up cycles, it will return to normal. Something I have considered is that a leaky injector might have something to do with this. If the injector drips after shutdown, then there would be some raw gas puddled in the intake runner or intake port that could cause high idel at start-up. A consistently leaky injector might cause a high idle until the engine warmed up enough for thermo expansion of the injector body forced the leak closed.

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It's possible, but I think a dribbling injector will usually produce a smoky startup and rough running, rather than a smooth high idle.

After re-checking vacuum lines and the intake (this time with TB cleaner, not propane) I found there to be major leakage around a couple of the intake studs (the front stud wasn't even finger tight!!). I re-tourqed them all except for #10 (it must have fallen off). Idle now sits at approx 900rpm after warm up when put in park/neutral. AWESOME. Thanks for all the help.

Check your throttle cable and throttle bellcrank assembly. On my 87, the wire in the throttle cable had cut a track in the sheeth, causing it to return to idle very slowly. Also the bellcrank fullcrum surfaces were well worn adding more drag to the throttle cable movement.

LynchMob, there's a coolant temperature sensor (CTS) located on the side of the block underneath the exhaust manifold. It sends coolant temp signals to the ECU and controls engine warm-up idle speed, ignition advance, and inhibits EGR operation when cold.

If the CTS is bad, it could cause a high warm-up idle. I don't know the values for it, but try checking the resistance from the terminal to ground, when the engine is both cold and warm. There should be a difference of several K ohms when it changes temperature.

Thanks for the (continuing) replies guys...but I've fixed the problem...

LynchMob said:

After re-checking vacuum lines and the intake (this time with TB cleaner, not propane) I found there to be major leakage around a couple of the intake studs (the front stud wasn't even finger tight!!). I re-tourqed them all except for #10 (it must have fallen off). Idle now sits at approx 900rpm after warm up when put in park/neutral. AWESOME. Thanks for all the help.

Click to expand...

Over the last two days the idle has improved still to around 750rpm in park/neutral...I'm guessing computer is adjusting to normalcy (sp?).


The CTS (and MAP) were my next sensors to diag/replace.