High Idle - Vac. Lines maybe leaking?

[Charlienofun]

I'm looking for things that would cause a high idle (1500 indicated) all the time. I removed the intercooler and unscrewed the air cleaner to get at the idle screw, I gave it a few quarter turns and it didn't seem to make any difference after I put it all back together, I don't have an 18inch screw driver but I will go out and get one today. I will also pickup a few extra parts I need to adapt a boost leak tester I have to the elbow under the CIS meter. I should also mention I checked the aav (I hope i'm not confusing that) and when I squeeze the hose the idle only drops a little bit def. not under 1000RPM indicated. I noticed that on my aftermarket (B&B I think) intercooler the boost line that I suspect goes upfront for the brakes (and in my case clock boost gauge) is blocked off. Was this an installer oversight? was that supposed to be drilled open for cars with power assist brakes etc...? Maybe I could just put a t on the line already on the other side of the intercooler for testing? any thoughts? hmm distributer vac canister is way rusty and looks very spent, both the vac lines seem to be connected with non leaking hose but I have not yet removed the pop off valve assembly to check the rest of the lines past this one electronic one. Can't I just unplug both the vac lines from the distributer to see if thats part of the effect? Please ignore that busted intercooler mount - I'll look for a new pop off valve housing soon (or change to later piping). Oh I should mention the car is an 87 930 with the extra air injection pump / veins removed.

[A930Rocket]

In your second pix, that line is vented to atmosphere just like it is.

Where does the boost line off the IC go to? Are you sure it goes to the brake booster/boost gauge? Boost gauge maybe, but I suspect it's not big enough for the brake booster.

Originally Posted by Charlienofun

I'm looking for things that would cause a high idle (1500 indicated) all the time. I removed the intercooler and unscrewed the air cleaner to get at the idle screw, I gave it a few quarter turns and it didn't seem to make any difference after I put it all back together, I don't have an 18inch screw driver but I will go out and get one today. I will also pickup a few extra parts I need to adapt a boost leak tester I have to the elbow under the CIS meter. I should also mention I checked the aav (I hope i'm not confusing that) and when I squeeze the hose the idle only drops a little bit def. not under 1000RPM indicated.

I noticed that on my aftermarket (B&B I think) intercooler the boost line that I suspect goes upfront for the brakes (and in my case clock boost gauge) is blocked off. Was this an installer oversight? was that supposed to be drilled open for cars with power assist brakes etc...? Maybe I could just put a t on the line already on the other side of the intercooler for testing? any thoughts?



hmm distributer vac canister is way rusty and looks very spent, both the vac lines seem to be connected with non leaking hose but I have not yet removed the pop off valve assembly to check the rest of the lines past this one electronic one. Can't I just unplug both the vac lines from the distributer to see if thats part of the effect?

Please ignore that busted intercooler mount - I'll look for a new pop off valve housing soon (or change to later piping).


Oh I should mention the car is an 87 930 with the extra air injection pump / veins removed.

[Ronnie's.930]

Hello - a very high idle that does not respond to adjustments made to the throttle bypass screw seems to often be caused by a failed deceleration valve . . . there are many threads about this problem floating around - here is one of them:

How to bypass decel valve?

[Charlienofun]

Originally Posted by Ronnie's.930

Hello - a very high idle that does not respond to adjustments made to the throttle bypass screw seems to often be caused by a failed deceleration valve . . . there are many threads about this problem floating around - here is one of them:

How to bypass decel valve?

Ronnie, I'm headed to the auto parts store to pickup the caps to block the decel valve ports, I'll post the results here later today!

I also tried to photo the boost line that I think is going to the front of the car, I have no real proof though and so far the vac. diagrams are not helping me at all. I have not fully removed the airbox yet in my troubleshooting so it could just be right out of sight but either way I assume it should be hooked up to something - I can tee it off one of the other boost lines easily enough but I'd rather understand whats going on... hehehe

[A930Rocket]

What ever it is, it isn't stock as there isn't anything going that way. Does it got to the charcoal canister in the right rear fender well by chance?

[Charlienofun]

Originally Posted by A930Rocket

What ever it is, it isn't stock as there isn't anything going that way. Does it got to the charcoal canister in the right rear fender well by chance?

I will be taking the IC off again tomorrow afternoon I'll move the ac compressor this time and remove the airbox and figure out where its going, if I get lucky with the other issues I might just hook it up and see if I can tell what changes....

[Charlienofun]

Originally Posted by Ronnie's.930

Hello - a very high idle that does not respond to adjustments made to the throttle bypass screw seems to often be caused by a failed deceleration valve . . . there are many threads about this problem floating around - here is one of them:

How to bypass decel valve?

Thanks for the lead, This afternoon I removed the Decel valve (well left it in but unhooked. I capped the line going into the "pop off valve assembly" and the the top part of the Y vac line but left the other side connected to the pop off valve. I also put a cap on the throttle body but left the line on the valve for looks (I have emissions testing coming up). After this the car wont start, not sure what I missed here are some pics of the work, Prehaps the check valve in the pop off valve vac line (the huge one that was split with the decel valve) was reinstalled by me backwards but I'm not sure why this would cause the car not to start, maybe some compressor surge if I didn't have the pop off working right but not start? I don't smell any fuel - I'll start with the fuel system fuses first tomorrow. anyone see anything I did wrong thats obvious?

Thanks

Charlie

here is the pop off valve capped up


Here you can see the Throttle body connection is capped, and the top of the T for the pop off valve itself and the decel valve port is capped off.

[Ronnie's.930]

Did you remember to re-connect the wire that goes to the overboost switch (that switch is mounted on the BOV body that you removed) . . . if the wire is not connected to the switch, and not grounded against anything, the fuel pumps will not run . . .

[Charlienofun]

Originally Posted by Ronnie's.930

Did you remember to re-connect the wire that goes to the overboost switch (that switch is mounted on the BOV body that you removed) . . . if the wire is not connected to the switch, and not grounded against anything, the fuel pumps will not run . . .

Ronnie, Thanks for the guidance! I really appreciate it, this is a really awesome forum! Can you tell me is A the overboost switch you speak of? what color should the wire be going to it (white?) I might have mixed up the wires although I tried to take pictures of before and after to keep from messing things up but oh well

[Ronnie's.930]

Yes, "A" is the overboost switch and the wire going to it is white . . . I'm not sure why that wire tab "B" is there - it looks like someone put that there so they could bypass the overboost switch (if you ground the white wire, the fuel pumps will run but you eliminate the protection provided by the overboost switch) . . . you might try hooking your white wire to "B" - if the pumps run when hooked to "B" but do not run when hooked to "A" that would probably indicate that the overboost switch is bad . . .

Ronnie

[911st]

The AAV is usually the first suspect when the idle jumps.

If you pull the vac line to the dist that faces the dist timing should jump about 300rpm from your vacuum retard function going away.

[Charlienofun]

Thanks for the sanity check! I remember hooking up the wire, but I also moved the gigantic blow off valve around a good bit while I was hooking up its vac line so its very possible I caught the sensor wire on something and it fell off or worst case mixed it up with the vac sensor for the dash gauge (but I really doubt this I kept them separate while I had it apart). I'll update the thread after I get my hands back in it.

Thanks again Ronnie

[Charlienofun]

Originally Posted by 911st

The AAV is usually the first suspect when the idle jumps.

If you pull the vac line to the dist that faces the dist timing should jump about 300rpm from your vacuum retard function going away.

is the AAV is the cast aluminum looking device that has the heating element that closes the little slide? The thing next to the WUR that lets air past the throttle body for warm up? I hate to say it but I have heard them all called the same thing and its all mixed up in my head from all the reading I have done sorry...

I tested this at first and I believe its working but I can easily plug it again if the idle is not dropping after it "closes"

I believe my distributer only has 2 vac lines, one runs through and electric valve (with a mercedes logo on the connector) and it has one line to atmosphere and one line I thought goes back to the throttle body. The other distributer vac. line runs to what I read is a thermo switch then itself runs to the throttle body - is the AAV one of these things?

[mark houghton]

[QUOTE=Charlienofun;4922199]is the AAV is the cast aluminum looking device that has the heating element that closes the little slide? The thing next to the WUR that lets air past the throttle body for warm up? QUOTE]

That's the little bugger! But technically it's called the AAR...since it infinitely regulates the amount of air, as opposed to being a Valve that's either on or off. It took me awhile to get the correct nomenclature through me head as well.

The AAV, on the other hand as previously mentioned...should it fail and continuosly let air into the manifold will result in a high idle that cannot be adjusted away. It's the gold colored flying saucer shaped thing tucked way back under the intercooler with two large hoses going to it and a small vacuum hose connected as well.

[Charlienofun]

Spent a few mins at lunch today looking over the car - The white wire is connected to the over boost switch and I tried just grounding it to the spade that is stuck on my BOV didn't make a difference. I thought I smelled fuel after cranking it for a while but It might have just been fumes it certainly didn't have any fuel coming out of the exhaust after multiple attempts to start it. There was a bit of corrosion on the bolts that hold the BOV into place, any chance its not making good enough a ground?

I guess the more important question now is does the over boost ground line also kill spark? I don't hear the CDI box making its whine with the key in or after I stop cranking, I just replaced the turbo timer relay for the CDI system and I am used to its high pitch whine but I def. am not hearing it right now. I checked the fuses in the front box, they all look good.

In a few hours I'll take off the Charge Cooler again and back trace all my steps hopefully I can find something really stupid I did or maybe the over boost wire is busted somewhere.

Thanks to everyone for helping me so far I'm understanding more about this car every day due to you guys!

[mark houghton]

Originally Posted by Charlienofun

Spent a few mins at lunch today looking over the car - The white wire is connected to the over boost switch and I tried just grounding it to the spade that is stuck on my BOV didn't make a difference. I thought I smelled fuel after cranking it for a while but It might have just been fumes it certainly didn't have any fuel coming out of the exhaust after multiple attempts to start it. There was a bit of corrosion on the bolts that hold the BOV into place, any chance its not making good enough a ground?

I guess the more important question now is does the over boost ground line also kill spark? I don't hear the CDI box making its whine with the key in or after I stop cranking, I just replaced the turbo timer relay for the CDI system and I am used to its high pitch whine but I def. am not hearing it right now. I checked the fuses in the front box, they all look good.

In a few hours I'll take off the Charge Cooler again and back trace all my steps hopefully I can find something really stupid I did or maybe the over boost wire is busted somewhere.

Thanks to everyone for helping me so far I'm understanding more about this car every day due to you guys!

The overboost sensor, in conjunction with the yellow overboost relay, shuts down only the fuel pumps when overboosting. So, when you were cranking away and not getting any fire - and smelling gas - now it sounds more ignition spark related.

If you want to check to see if your fuel pumps are running, simply turn the ignition on, pull the blue electrical plug from the top/back side of the fuel distributor...and the pumps will light up. Now pull the white wire from the boost sensor, and the pumps should stop. Ground that wire, and the pumps should start back up. If no pump issues show up after following those steps, then assume ignition.

[Charlienofun]

Originally Posted by mark houghton

The overboost sensor, in conjunction with the yellow overboost relay, shuts down only the fuel pumps when overboosting. So, when you were cranking away and not getting any fire - and smelling gas - now it sounds more ignition spark related.

If you want to check to see if your fuel pumps are running, simply turn the ignition on, pull the blue electrical plug from the top/back side of the fuel distributor...and the pumps will light up. Now pull the white wire from the boost sensor, and the pumps should stop. Ground that wire, and the pumps should start back up. If no pump issues show up after following those steps, then assume ignition.

Thanks Mark, I just got done going over everything again. Good news is that its running now I'm really not sure what I did this time around that made it run to be honest.

I took a hard look at the white over boost sensor wire, its looking rough it will need to be clipped and have a new lead soldered on soon I twisted the wire and stuck it back together. The only other thing I noticed is that I might have pinched the distributer vac line that goes to the thermo switch then to throttle body.

It was weird though just as I expected key in and this time around I hear the CDI box whine, it fires right up.

Now the idle quickly shot up to about 1350 RPM - after a few mins the idle lowered down to 1200-1300. Once it got down that far I figured the AAR should be shut, I went and pinched the hose from the intercooler to the AAR and it the engine speed didnt drop any further (at least not that I could detect).

I'm headed back soon to try and lower the idle with the bypass screw hopefully I can get it down around 950!

[mooney265]

[QUOTE=911st;4922125]
If you pull the vac line to the dist that faces the dist timing should jump about 300rpm from your vacuum retard function going away.[/QUOTE]

Did you do this?

You did mention that part of your distributer was rusted/corroded... maybe it's the vaccuum advance portion. therefore, your timing is too far advanced at idle causing the higher idle speed???

Just a thought...

[Charlienofun]

I adjusted the idle screw and got it to sit at 950RPM after warm up! It took forever because I couldn't track down an 18" screw driver I had to pop the air cleaner off each time to get at the screw

I still would like to figure out what kept the CDI from doing its thing the first time around. oh well maybe later on I can pull the white wire to fix it and see if that yellow relay is working.

[Charlienofun]

[QUOTE=mooney265;4923826]

Originally Posted by 911st

If you pull the vac line to the dist that faces the dist timing should jump about 300rpm from your vacuum retard function going away.[/QUOTE]

Did you do this?

You did mention that part of your distributer was rusted/corroded... maybe it's the vaccuum advance portion. therefore, your timing is too far advanced at idle causing the higher idle speed???

Just a thought...

Nope I never messed with the distributer vac lines besides verifying they were hooked up correctly and the hoses weren't leaking or falling apart. The vac valve on the distributer itself is nice and rusty one of many things i'll be trying to replace.

I'm thinking I need to get a CIS pressure gauge kit and get my wideband 02 installed so I can check the mixture.

Thanks everyone for all the guidance so far I'll post up again later when I get the wide band going or if I figure out what I did the first time I reinstalled the BOV and the ignition wouldn't fire.

Thanks! Charlie