Another 3.2 idle issue

Roswell · 04-10-2018, 12:51 PM

The car is an 88 Targa with 112000 miles.

In April/May of last year the clutch was replaced, bushings in the shift linkage replaced, heads pulled, valve job, new rings and a Steve Wong chip. Work was done by a reputable shop in ATL and ran great. Car idled at 800 rpm.

This past fall the engine would rev up and down until it warmed up. I did not address this issue until now. New Idea Control Valve, new O2 sensor, mixture adjusted.

The engine is just off. It never idles below 1000 rpm. This is the weird thing, when you remove the oil tank cap the idle does not drop.

Leak down test is scheduled for later this week. Any thoughts?

Nick Triesch · Nick Triesch's Garage

Vacuum leaks. Check everything. Every hose, every hose clamp. Intake runners.

darrin · 04-10-2018, 01:09 PM

" when you remove the oil tank cap the idle does not drop." This suggests a vacuum leak -- unmetered air would cause much of this -- (oops, nick t beat me to it)

Unclear whether you want to tackle yourself or take it back to the dealer and let them find the vacuum leak/culprit.

Roswell · 04-10-2018, 01:16 PM

Shop will do the work. Just want to understand what may be the issue.

gwinnch · gwinnch's Garage

When it warms up it stops reving up & down?

Roswell · 04-10-2018, 01:58 PM

The revving up and down stopped when I installed the new idle control valve and O2 sensor. The problem now is it just revs weird – never below 1000 RPMs and the whole pulling the oil cap off and no change in the revs is really throwing me.

darrin · 04-10-2018, 02:22 PM

When you take the oil cap off of a motronic 3.2 engine that has no vacuum leaks, you're introducing a new vaccum leak that will affect idle speed. Having no change in idle speed when you remove your oil cap suggests that another vacuum leak has already affected the idle speed.

As you increase the speed of engine (allow it to suck more air in through the throttle body), the percentage of air attributable to the vacuum leaks decreases, highlighting the issue at idle (I presume your car operates OK while you drive it). Vacuum leaks need to be identified and resolved and then idle speed (and idle mixture) need to be readjusted to "normal" -- while you could readjust the idle speed and mixture now, doing so without finding/fixing the vaccum leaks will leave your mixture wonky at higher load/revs.

Roswell · 04-11-2018, 03:24 AM

Thanks to all for your replies. Car goes into the shop today.

steely · 04-11-2018, 05:08 AM

open idle switch?

Jp-oh · Jp-oh's Garage

Vacuum leaks and electrical issues are my generic automotive nightmares. I have a vacuum issue too and am really dreading sorting it. I have gaskets and spacers laying around for the intake but all the various lines are what really make me queasy.

famoroso · 04-11-2018, 06:30 AM

I am not chasing a vacuum leak, but it has been suggested to obtain a cheapie smoke machine offa eBay. Introduce the smoke into the vacuum line for the power brake booster at the engine and easily find any / all vacuum leaks as a result.

Eric H · Eric H's Garage

I’ll second steely’s suggestion about the idle switch. It’s actually a pretty fine adjustment and it needs to be checked after any engine drop. If it’s not switching the engine “idles” around 1300rpm I think it is. Easy to check and it’s all detailed in the Bentley book.

darrin · 04-11-2018, 07:53 AM

Quote:

Originally Posted by Eric H

I’ll second steely’s suggestion about the idle switch. It’s actually a pretty fine adjustment and it needs to be checked after any engine drop. If it’s not switching the engine “idles” around 1300rpm I think it is. Easy to check and it’s all detailed in the Bentley book.

Eric/Steely -- is there any correlation between the idle switch and the OP's issues with the engine revving up and down and the idle speed not changing when the oil cap's removed?

Roswell -- please let us know outcome

Roswell · 04-11-2018, 08:13 AM

Car is in the shop with an "Old Pro". I will keep the thread updated.

Eric H · Eric H's Garage

Hi darrin - not sure about the hunting/vacuum leaks and ICV. At least when warm,though, if the ICV isn’t switching it will “idle” high. My point is it’s an easy check and I’d certainly verify ICV operation before chasing after other things.

darrin · 04-11-2018, 08:44 AM

thx eric and agree, easy check/confirmation to do. Just trying to build full picture in my mind so I can tackle if/when needed

GK81 · GK81's Garage

A DME car will hunt upon start-up after the battery has been disconnected. It has an Adaptive Memory. After driving it this hunting goes away.

However, what the OP is describing sounds like a vacuum leak. I think if the idle micro switch is open the idle is much greater then 1000.

steely · 04-11-2018, 11:21 AM

Quote:

Originally Posted by darrin

Eric/Steely -- is there any correlation between the idle switch and the OP's issues with the engine revving up and down and the idle speed not changing when the oil cap's removed?

Roswell -- please let us know outcome

Just to respond, I agree with Eric's response.

If one were expecting a closed sw for idle but it was instead open, the DME would stop regulating the idle and the rpm rises (per bentley somewhere) 500 rpm over the idle setting. I think the Bentley also cites 1300 rpm? That was my rationale.

I know it's a little contrary to answering the up & down revving problem, I only threw that out there b/c he mentioned the 1000 rpm mark and figured maybe....

And I saw that he already committed to go the shop, so I didn't invest in a big answer.

msterling · msterling's Garage

Check for loose bolts holding down the intake manifold. Common reason for air leak on 3.2 Carreras. Mine were loose.

Steve W · Steve W's Garage

Just to clarify, the 3.2 DME is not adaptive. Adaptiveness started with the 964. A misadjusted idle mixture 3.2's idle can improve when warmed up because the O2 sensor warms up with 2 minutes and trims/adjusts the ilde mixture to Lambda 1.0 which stabilizes the idle from an excessively lean or rich mixture.

With a high idle speed at idle, if it's not an intake air leak, the first thing that needs to be checked is the activation of the idle microswitch. When it does not activate at idle, the DME stays in part throttle mode thinking your foot is on the gas, and the engine wants to go. Depending on what chip you have in the car, the idle being in part throttle mode can be anywhere from 1200-1800 rpm. Many times, with a bad idle switch, a tech who doesn't check the switch, may inadvertently turn down the base idle screw down to bring it down to 800-900 rpm, in which case it will be turned down too much when the switch is fixed, causing the car to idle too low and/or stall out. Or in the cases of some of my customers, a owner had a stock or other aftermarket chip that had its idle adjusted to compensate for a bad idle switch, but when changing to my chip, the idle is up to 1700 rpm or higher, because the car really wants to go. Below you can see a picture of the idle switch, which is mounted on the throttle body, and a page from the Bentley manual on checking and adjusting it. The switch mounting bracket may just need to be adjusted up for the button to be activated by the steel arm, or the linkage may be adjusted too tight, not allowing the arm to positively activate the switch button, or the switch could be faulty.