2200rpm idle & stumbles around 3200 when driving, making progress, idle down to 1100, still stumbles above 3k Options

[RazorbackFan78]

Hey guys - I'm trying to track down the cause of my high idle.


I've checked the TPS and I get 20 clicks pre-ignition

I've pulled the AAR, soaked it in PBlaster, froze it, put 12v through it, confirming it opens and closes correctly. It also tested around 17ohms

I cleaned grounds at headlights, battery neg, driverside engine bay, and visually confirmed trans strap is brand spankin' new (thanks Curt)

Now i'm checking hoses for vac leaks and only one seems to drop the idle (drops it to a steady 1100rpm). It's the hose from the airbox elbow that Y's into the AAR and dizzy. See picture.

Is this sounding like my dizzy could use a good cleaning? I have other items on my troubleshooting list like MPS, fuel filter and decel valve but wanted to check in with you guys after discovering the vac issue. Thanks for your input. I'm still fairly new to this type of engine....so I'm learning as I go (IMG:style_emoticons/default/biggrin.gif)


BACKSTORY: for those of you who like a novel....car had points and idle would bounce between 100-900rpm more often than not. Anytime I'd reach 3200rpm while driving it would studder and loose power, in all gears, and it would also occasionally do it under a heavy foot at lower rpms. I replaced points with Pertronix 1847V and now the cold idle sits on 1100 like a rock for the first minute or so, then over the next minute it climbs to 2200 and holds steady. It still studders around 3200 when driving and occasionally does it at lower rpms when I'm really on the pedal.

[913B]

That is just filtered air supply from the air cleaner for the AAR. It is before the throttle plate so it should not matter, but I cant explain your high idle. I have been chasing my high idle as well for a long time. (IMG:style_emoticons/default/popcorn[1].gif)

[76-914]

Vacuum leak. Did you say the AAR is on that same line that when crimped the idle returns to normal? If so, my $$ is on the AAR that is alleged to be good.

[era vulgaris]

That hose doesn't Y to the AAR and the dizzy. That hose Y's to the AAR and the deceleration valve. You might want to make sure your hoses are routed correctly.

The hoses that connect to the dizzy vacuum canister are the small ones on the throttle body.

[RazorbackFan78]

Oops my mistake - you're right, the Y is to the AAR and decel valve.

That hose doesn't Y to the AAR and the dizzy. That hose Y's to the AAR and the deceleration valve. You might want to make sure your hoses are routed correctly.

The hoses that connect to the dizzy vacuum canister are the small ones on the throttle body.

[RazorbackFan78]

So the AAR did work outside of the car when I tested it but just to be sure it was working in the car, this morning I connected it directly to the battery. Measured 12v, and after a couple of minutes the idle only climbed to 1600. So that's new...It had been reaching 2200 before. The AAR was nice and hot so I pulled the hose, put my thumb on the AAR inlet and didn't feel any suction. Something else worth noting is that when I close off the airbox inlet with my hand, it dropped to 1100. It did this a few times. In theory, if I didn't have any vac leaks, shouldn't it have stalled or died when I covered the airbox inlet with my hand?

Appreciate the help guys.

Vacuum leak. Did you say the AAR is on that same line that when crimped the idle returns to normal? If so, my $$ is on the AAR that is alleged to be good.

[TheCabinetmaker]

Matt. Your aar should not be drawing air when hot and closed. It's fine. Set your idle hot. Sounds like you still have a vacuum leak.

[DRPHIL914]

my bet is on a vac leak -- have you replaced the intake runner boots? that is where I had problems with mine chased my tail with high idle for a while until I did those and the throttle body gasket. .

- you could spray a bit of carb cleaner around the intake runners, if its leaking your idle will change.

[76-914]

Disconnect all vac lines except the one to the MPS. If it now idles normally, add one line at a time until the idle jumps up. FWIW, the AAR is only needed the first few min's. After about 5 min's of warm up it won't matter much so you could bypass it.

[RazorbackFan78]

Curt - Sorry for the confusion, I agree that the AAR is working properly (I mentioned it didn't have suction after it was hot & closed).

I'll move onto hunting down the vacuum leak. I really really can't tell you how much I hope I don't have to resort to the spraying carb cleaner method. The engine looks so nice and clean!!!

[era vulgaris]

What kind of condition are the intake manifold gaskets, intake manifold boots, throttle body gasket, and oil filler gasket in?
You do have the phenolic intake manifold gaskets right, not the paper ones?

Have you checked the pcv valve on the filler tower for proper operation?

I had the same problem on my old 1.7. Trying to remember everything I did to fix it.

I'd follow 76-914's advice. IIRC that's how I found my vac leak. One thing to add, is that when you disconnect the vac lines from the plenum, you need to plug them. Otherwise you'll have a massive vacuum leak!

[rhodyguy]

Do 1.7s have the stacked elbow like the 2.0s? They can crack in areas you can't see at a glance.

[Bleyseng]

No,

[Dtjaden]

There is an additional possibility - the throttle plate may not be closing completely. You should be able to see this visually if the air cleaner box is off. You may also be able to force it closed by hand.

[RazorbackFan78]

So maybe I'm not understanding you correctly because I just removed all the vac lines I could see except the one to the MPS and when I started the car it jumped to 4k rpm instantly which scared the bajeebus outta me so i shut it down in fear of doing something wrong. Is that supposed to happen?

Disconnect all vac lines except the one to the MPS. If it now idles normally, add one line at a time until the idle jumps up. FWIW, the AAR is only needed the first few min's. After about 5 min's of warm up it won't matter much so you could bypass it.

[76-914]

You need to cap the open lines going to the engine. Otherwise you have the largest vacuum leak ever.

[RazorbackFan78]

Thanks for bearing with me guys. I think we're getting close. Here's an update.

I disconnected all hoses, inspected, reconnected. It's now sitting around 1200 +/-100 but it no longer climbs up to 2200 anymore when warmed up. So that may be a small victory. But idle spec is 900 right?

So I took the airbox off and immediately started hearing a distinct hissing sound which I don't hear when the airbox is on. The hiss seems to be coming from the left side of the plenum/throttle body area. Also, I noticed a couple of flame puffs in that same area when I was using propane to try and detect leaks. Yes, the propane ignited briefly. Only a tiny puff or two, but I decided to put the propane away and focus on that area.

2 Questions:

1. When I cover the airbox's intake with my hand, the car continues running with barely a noticable drop in idle. But when I remove the airbox and cover the intake the car dies immediately. Is the goal to have an air-tight airbox? It looks like the only two hoses connecting to it are for filtering air, not maintaining a vacuum. Just making sure I'm ruling out the right things.

2. Is the hiss and propane ignition near the throttle body/plenum possibly a good indicator of a vac leak? Maybe a TB gasket or the plenum itself? I wasn't expecting my propane to ignite. Kinda spooked me.

Thanks guys!

[76-914]

That hiss is normal when the air filter is off. You should also check the metal box aka plenum, that the throttle body sits upon. They rot out. You can remove it and fill with a liquid to check. Also, check the bushings and shaft on the throttle body butterfly/plate shaft for slop. IIRC, The only source of ignition in that area that might light off propane is the cold start valve, aka the 5th injector. 1100rpm is OK. Especially if your engine is "tired".

[Chris Pincetich]

I disconnected all hoses, inspected, reconnected. It's now sitting around 1200 +/-100 but it no longer climbs up to 2200 anymore when warmed up. So that may be a small victory. But idle spec is 900 right?

That's pretty good. (IMG:style_emoticons/default/beerchug.gif)
Have you gone for a test drive? Get out and enjoy it before the next thing goes wrong! (IMG:style_emoticons/default/dry.gif) (IMG:style_emoticons/default/biggrin.gif)
If things stay stable, and the idle is just a bit high, just try to adjust that via the idle screw on the throttle body or the knob on the ECU, depending on your set-up.

[RazorbackFan78]

Glad to read that the hiss is normal with the air cleaner off. One less thing for me to worry about. Sometimes I really do feel like a doofus compared to you guys when I'm working on this car (IMG:style_emoticons/default/blink.gif)

So anyway, before I go pulling off the TB & Plenum to check for leaks, I thought I'd quickly try disconnecting the TPS to see if my 3000rpm stumble went away (I'd read a few other posts where people recommended disconnecting it to determine if it was the cause of the high rpm/WOT stumbling. I disconnected it and took it for a spin. Engine seemed to run strong all the way to 4k but then started a small studder...not as bad as when it did it around 3k. But UGHHH the idle climbs to 2200 now and stays there unless I drag it back down with the clutch. Then it sits at 1100 for 20-30 seconds and climbs back up to 2200. Anyway, I'll reconnect TPS and see if it goes back to idling at 1100 and studdering at 3k.

The company I work for is Jewish-owned and operated which means I'm off for the next four days. Woohoo!!! Hopefully I can the gremlins worked out by then.

I'm trying to stick to the one-change-at-a-time mantra!.