Goofy idle slowing down at intersections

[1985RedTarga]

My 85 Targa has recently been acting goofy lately. Here's what happens...when driving at speeds of 45+ and approaching a turn or a red light, I'll take her out of gear and the idle will rev up and down (about 100-200 rpms, back and forth) for about 3-5 seconds. This all occurs around what I call a normal idle of 1000 rpms.

If I'm driving in a neighborhood, 25 mph and come to a turn or a stop, it doesn't act weird at all. It all seems to happen at the higher speeds/rpms. I thought maybe it was some bad fuel. I ruled that out. It first happened about 3 weeks ago during a heavy rain. Since I hardly ever drive it in the ran, I thought maybe some water got down the engine vents and was causing something to act odd. But for the last couple of days it's been driven rain free and still does it.

The engine was rebuilt 2k miles ago (top end) and has performed awesome, with the exception of the last couple of weeks and the idle thing. Minus the periodically odd idle, it runs great!!

Baffles me!! Anyone with advice??

Jamie

[Dave Colangelo]

A good place to start with idle issues is new plugs new rotor and distro cap, a new air filter, and a new fuel filter. These Items are cheap and can be but in quickly and in my experience have solved what seem to be serious ignition issues. Give it a shot and see if that takes care of it.

In terms of the rain obviously water in fuel is bad as im sure you know. The old CIS systems were very susceptible to moisture issues but if you have an 85 I believe that has the EFI which I dont know much about. It could also be your injectors or injector O rings.

Regards
Dave

[JTL]

My car also has the same issue and a hard start to boot. My bet is on the idle control valve(ICV). Just haven't had time to check it yet. There is a test procedure and resistance values to check.

Bentley says 40 Ohms between the outer 2 terminals and 20 Ohms between the middle and either side terminal.
A quick check came up with some off spec #'s for me. I need to pull it soon and take more time with it.

A new ICV is $100 +/-. Hopefully this it the problem -- we'll see...

[DRACO A5OG]

Next time it "Hunts" at idle, pull over, leave the car on, secure the e-Brake, lift lid and take a screw driver and tap the Idle Control Valve (ICV). if she clears up then your ICV is clogged and need cleaning.

After cleaning, check the ohms

[86 911 Targa]

Originally Posted by DRACO A5OG

Next time it "Hunts" at idle, pull over, leave the car on, secure the e-Brake, lift lid and take a screw driver and tap the Idle Control Valve (ICV). if she clears up then your ICV is clogged and need cleaning.

After cleaning, check the ohms

That's what I would do.

[john walker's workshop]

it may do that because you say your normal idle is set at 1000. it should be 800. try it.

[1985RedTarga]

About 6 months ago, during the rebuild, all the plugs, filters, cap etc, were changed. It said in a sad state for a few years. So that rules that out.

Upon looking further at the normal idle speed, it's about 900. So that seems close enough.

After driving a little more driving today, it's just not at higher speeds. It seems to do it at any speed. I can get it to do it 75% of the time if I quickly pull my foot off the gas and take it out of gear. That's when it does it. Almost like it's as the rpms drop, it acts up at about 1000k.

I'll have to get my books out and try the ICV suggestions.

Drago, what do you use to clean it and any tips? I suppose if the cleaning fails, I can try the electrical stuff, but my tools are back in New Mexico and I live in Ohio now.

[Tippy]

Kick back, grab a 6-pack, and search key words like "idle surge", idle hunt", etc.

This is a very common problem with these cars (C3.2's).

I'll warn ya though, you will become a hypochondriac!

[DRACO A5OG]

Service of the ICV:

Remove and check to make sure the internal components will rattle freely when you vigorously twist/rotate back and forth.

Use a non-residue Carb Cleaner. You will notice that is plenty of soot will coe out, continue until the fluid comes out clear. Let dry out then use some silicon based spray lube, just a touch to help lubricate the internals. Let dry.

Now check the internal movement, it should free up nicely.

Use a Digital Volt Meter ( borrow one, I am sure a neighbor has one ), PLace Black lead on center and measure the two sides for proper OHMs per Bentley.

If this fails move to the Idle Position Switch, pull and release gently the throttle arm. Listen for a proper click at rest.

As far as reading the TACH on our babys, remember the RPM tics start at 200, 400, 600, 800 then 1000 the hash mark.

If you are seeing the needle at the first hash below the 1000 mark that is 800 RPMs. if in between the hash and 1000 mark, you are at 900RPMs.

Stock 84-85 3.2 the RPM is 780-800 RPMs, 86-89, or chipped is 880-900 RPMS.

You must adjust idle by jumpering B&C and when the car is fully warm 190-195 degrees.

Hope this helps Brother.

Jim

[kidrock]

I'm definitely with Jim and JW on this one. However, you did mention that this occurred after a heavy rain. Just for schitts and giggles, remove your distributor cap, and clean and dry it thoroughly. See if that helps. Cleaning the ICV is a snap, though. And your idle should be set at 800 rpms, very basic to do and satisfying for the first timer.

[1985RedTarga]

I finally got my multi-meter in hand. While I was waiting, I bought a used ICV and swapped them out. Same freakin' problem!!! Both the old and new ones cleaned and lubed. Didn't help.

So the next step is to do some electrical testing. God help me, the idiot!!

So I'm going to check the Ohms huh? What the hell are they? And I'm testing the actual ICV, not the wiring harness?

Keep the help coming boys!!

[JTL]

I finally took some time to fully check the icv. The resistance values, i.e. Ohms, check out as does the mechanicals.
I've been driving the car like this for a while. The problem seems to occur every time I push the clutch in when the enginer is cold. It does happen when warmed up but less often.
Could this be an O2 sensor or head temp sensor problem? I remember changing out the O2 ~10 years and 50k miles ago. The head temp sensor has never been changed.

[Flat Six]

Originally Posted by 1985RedTarga

It first happened about 3 weeks ago during a heavy rain.

Jamie -- pull the distributor cap and clean/dry the cap & rotor. Make sure you re-seat the cap flush. Then one by one pull / dry (compressed air works great for this) each end of each spark plug lead (cap end and plug end). Don't forget the coil wire too.

I'd bet you a cold frosty microbrew that'll help.

Good luck

Dale

[Flat Six]

Originally Posted by 1985RedTarga

So the next step is to do some electrical testing. God help me, the idiot!!

So I'm going to check the Ohms huh? What the hell are they? And I'm testing the actual ICV, not the wiring harness?

[1985RedTarga]

Originally Posted by Flat Six

Jamie -- pull the distributor cap and clean/dry the cap & rotor. Make sure you re-seat the cap flush. Then one by one pull / dry (compressed air works great for this) each end of each spark plug lead (cap end and plug end). Don't forget the coil wire too.

I'd bet you a cold frosty microbrew that'll help.

Good luck

Dale

Dale, I did pull the cap and rotor off yesterday while tackling another project, and they were totally dry. Now I didn't do each boot on the cap yet, but there's no signs of water anywhere. But for giggles, I'll try it tomorrow.

[DRACO A5OG]

Okay, next, let's check your base idle:

Use a piece of 4" wire and jump connectors B&C at the round relay socket left side of engine bay.

This will insure you are at proper base idle for our year Stock is 780 RPMs and chipped is 880RPMs. Remember the tach starts at the 200 mark, then 400, 600, 800 and 1000. If stock you need to be a just below the 800 hash mark and if chipped just below the middle of 800-1000 mark.

She must be at 194 degress or hot when checking base idle.

Note: reading the tach without doing the jumpered B&C will not be accurate due to the fact the DME via O2 Sensor will constantly compensate.

Compliments of 911chips: http://www.911chips.com/C1INSTR.pdf page 3

I would also check the idle switch at the throttle body, carefully pull back on the throttle, pinching the arm not placing your finger behind it (this will keep the cruise control cable from bending) and slowly release to see if you can hear the click of the switch. Car off so you can hear the click.

This is an opportune time to check if throttle is sticky/binding. My throttle bushings at the intake assembly was shot causing infrequent binding and not allow the throttle to seat completely to trip the idle switch. I posted a fix.

Jim

[1985RedTarga]

Originally Posted by DRACO A5OG

Okay, next, let's check your base idle:

Use a piece of 4" wire and jump connectors B&C at the round relay socket left side of engine bay.

This will insure you are at proper base idle for our year Stock is 780 RPMs and chipped is 880RPMs. Remember the tach starts at the 200 mark, then 400, 600, 800 and 1000. If stock you need to be a just below the 800 hash mark and if chipped just below the middle of 800-1000 mark.

She must be at 194 degress or hot when checking base idle.

Note: reading the tach without doing the jumpered B&C will not be accurate due to the fact the DME via O2 Sensor will constantly compensate.

Compliments of 911chips: http://www.911chips.com/C1INSTR.pdf page 3

I would also check the idle switch at the throttle body, carefully pull back on the throttle, pinching the arm not placing your finger behind it (this will keep the cruise control cable from bending) and slowly release to see if you can hear the click of the switch. Car off so you can hear the click.

This is an opportune time to check if throttle is sticky/binding. My throttle bushings at the intake assembly was shot causing infrequent binding and not allow the throttle to seat completely to trip the idle switch. I posted a fix.

Jim

Jim, when you are referring to jumping B and C, what are you saying? Is that in reference to the photo Flat Six posted? Would alligator clips on the wire make it easier?

Jamie

[86 911 Targa]

Originally Posted by 1985RedTarga

Jim, when you are referring to jumping B and C, what are you saying? Is that in reference to the photo Flat Six posted? Would alligator clips on the wire make it easier?

Jamie

Here.

[1985RedTarga]

I think I have FINALLY fixed the problem. Otto from Pelican Parts emailed me and told be to tighten all the bolts in the intake. So looking around there, I found a loose hose clamp for the hose that runs from the intake to the idle control valve. It was the original crimp style that some how had seen it's day and was loose. So I go to Ace and get a new clamp. The problem seems to be solved. I tried several times to replicate the problem, but couldn't. And now my idle is at 8k rpms, as it should be. I'm keeping my fingers crossed that this is it, but I do feel pretty good about it. I knew it was something so simple. Thanks so much to the Pelican family!!

[DRACO A5OG]

Nice, I know you meant 800RPM's

Yeap, it always seem to be the simple stuff Vacuum Leak, you are lucky you found it so quickly.