how to raise idle rpms a nudge?

[BerniniCaCO3]

Hi!

Minor gripe to work out; probably an easy fix.
At idle sitting in traffic my car shakes a bit. There's just some harmonic vibration that causes it to rattle a little quicker than once a second.
I was asking a coworker (I'm @volvo) about it, and apparently some '90s models with the inline 5cyl had similar complaints, and it really does just come from harmonics and idle rpms being low. The turbo versions of the engine idled higher and picky high-maintenance volvo customers did not complain about them vibrating.
Seriously: I just got a car Friday where the customer complains that the starter "shakes" the car (well, yes, it's kicking the engine to life... you might see a ripple or two in your starbucks coffee), and that the a/c makes noise (well, yes, a fan moves air, and moving air makes noise)... In this case, it was a 10,000 mile brand new car with no issue at all. Obviously there are a/c compressors whose bearings go out, fans whose bearings go out, etc., this was not one of them.
Moving on.

If my tach is telling the truth, I'm idling at <300rpm, kinda low! That said, I don't know how much I trust its precision at the lowest end of its readout, so I might not be idling *quite* that low. *shrugs* who knows.
Unless the sort of tach that gets its reading directly from the distributor is always spot on.

If I nudge the gas and bring it to 500rpm it gets much smoother, and if I bring it to 600, 750rpm the vibration goes away completely.

So! Now I'm wondering how I can raise the idle rpms.
theoretical naive option (a): advance that throttle plate backing screw clockwise, so that even with my foot off the gas, it gets a little bit more air.
theoretical naive option (b): I've now got an explorer/mustang hybrid engine, with the original lopo IAC. If they fit, which I seem to remember they might not have... install a mustang or explorer IAC?
theoretical naive option (c): could tv cable pressure have anything to do with idle speed?

option (d): it's really no rougher than any true pickup, just live with it.

[rellik god]

Corrected Base Idle Reset

Summarized/Corrected Base Idle Reset version


1. Clean TB with carb cleaner and nylon brush (toothbrush size). Engine off, fully open TB blade and spray/brush TB until all gunk and oil residue is cleaned.

2. Allow to dry, or close TB blade and start engine until it clears all carb cleaner fumes/liquid.

3. Let engine idle...if it doesn't, increase idle speed via TB stop screw until engine stays idling on its own.

4. Disconnect IAC valve, if engine dies repeat 3 with IAC disconnected.

5. Set idle speed to the lowest setting possible between 600-800 rpms with IAC disconnected. It is key to use the lowest possible to prevent idle surge, rolling, etc once the IAC is connected as follows.

6. Turn engine off, and reconnect IAC

7. With Ign On Eng Off, check TPS voltage output....if it's between .7vdc - 1.0vdc, it's OK. This voltage check should be done between the Green and Black wires at the TPS side connector as shown in the pic below....(-) terminal of the DVOM on the Black wire and (+) terminal on the Green wire.




8. Disconnect battery (-) for 3-5 minutes.

9. Reconnect battery, start engine, allow it to idle for 2-4 minutes to confirm setup,

10. If idle speed falls too low or stalls, increase idle speed via the TB set screw a little at a time.

11. Turn engine off for 20 seconds, re-start engine and repeat 9 - 11 if required.

12. Reconfirm TPS output is within the .7vdc - 1.0vdc range.......you're done!...

..no need to reset ECM KAM (reset computer) b/c the TPS minimum value used for idle control, is automatically reset by the EEC-IV every time the ign is cycled on-off for 20 seconds-on, and as explained in the next post

13. Allow a 10-20 minute "relearning" period under normal driving conditions (drive cycle).....now you're done.

got this from sbftech site

[86VickyLX]

What the fuck? I doubt it's idling that low. 300rpm, it cannot run. That's about the RPM it's at when cranking lmfao. Your tach is shit. I'd go by a tach that is set right. Any codes when you run a code scan?

[BerniniCaCO3]

thanks rellik god!

Yeah, it's sunpro, of course it's shit. Probably the scale just isn't calibrated; wonder if I can simply rotate the dial?
Although sunpro IS a snap-on subsidiary, and snap-on is good as gold... just kidding.

Whether 300=300 or not, no, I never did reset the idle, I didn't even realize there was a particular manual procedure, so I'll go ahead and do that!

[86VickyLX]

Yeah, the idle relearn thing is good if you don't have the patience for the car to learn it on it's own.

Some of those Tachs have switches where you can swap from 4, 6, 8 cylinders. Others require you to twist two wires together to make it read right on an 8 cylinder?
Btw, for the best results. Set the TPS voltage as close to .9 volts as possible.

[gadget73]

Target idle is like 670 rpm. If its running there, theres no need to monkey with it.

[BerniniCaCO3]

oh, the car will learn on its own? How long does that take?
It might already have.
The only tiny bit of strangeness is when I first start it up, it'll rev (for just a second) to 2k, then drop to 500, then rev back up to 1k, then settle steady at "300," In the span of a couple seconds really.
I figure that's just normal for cold start up.

Advancing the TB set screw logically increases idle speed, right?
It might just be too far backed off.

I used to have, from buying an old guy's toolbox, an old multimeter with dwell. Wish now that I'd kept it; that could give me a true rpm reading.
I do have it set on 8cyl. In fact, since what it's doing is reading that 8 pulses = 1 revolution, if I were to set it on 6 or 4 cylinders, it would just read 50% or twice as fast respectively.
Hah! I could impress (very gullible) friends by setting it to 4cyl and showing off how my engine can rev to "8000rpm" no problem!

[johnunit]

Maybe use a timing light with tach to figure out true rpm.

[BerniniCaCO3]

I didn't realize that they made them! I might look into that.
Curiously, it would seem that No One owns even a plain timing light anymore. They've been obsolete for too long... I'd tried asking around the shop before and must have talked with a dozen techs ;-)

[BerniniCaCO3]

Hah! Was looking under the hood for something else, and noticed that the clutch fan is cavitating. Seems the clutch itself --just one year old!-- has some wobbling play in it, and, where it bolts to the pulley actually might be bolted off-center too... though how that's even possible I can't say.
Time to put in an electric fan. I've already got one and the thermostat to control it; just been waiting in the wings for me to get off my ass and install it.

It would certainly explain my idle-speed vibration, more noticeable at slower harmonics when it can drive something I can feel in my seat.
I'd swear it's something new; are clutch fans not made to run at 5000 rpms? Or, are bottom-priced autozone clutches not made to run at 5000 rpms and/or greater than one year?

[86VickyLX]

oh, the car will learn on its own? How long does that take?
It might already have.
The only tiny bit of strangeness is when I first start it up, it'll rev (for just a second) to 2k, then drop to 500, then rev back up to 1k, then settle steady at "300," In the span of a couple seconds really.
I figure that's just normal for cold start up.

Advancing the TB set screw logically increases idle speed, right?

Yes opening the Throttle more will increase RPM. Though, your best bet is to keep it as close to closed throttle as possible.
I still think that that tach is wonky. 300rpm the car shouldn't be idling at all lol. The rev high, low, high low, sounds like an IAC issue. If you unplug the IAC, what does it idle at? Or does it stall?

What is your timing set at?
What is your tps voltage set at?

[BerniniCaCO3]

timing is at 10BTDC.
Need to look at the tps. I worked today.

[gadget73]

where it bolts to the pulley actually might be bolted off-center too... though how that's even possible I can't say.

Did you put the bushing back in the fan clutch? There is a small brass bushing that sits in the fan clutch to locate it on the water pump shaft. if thats missing, you'll never get the clutch centered properly and it will do this. BTDT. I had a bushing made from a scrap piece of steel pipe.

[87_crown_vic]

i adjust timing to 12* instead of 10* when doing adjustments, remove the spout connector... clean up the IAC as suggested and dont touch the throttle set screw unless the throttle butterfly is jamming/sticking when you go to press gas... even then, try to clean the throttle body up inside...