More D-Jet, High Idle Lean Mixture Options

[ggress]

Just getting a '74 2.0 running that I purchased few years back. Replaced all fuel lines, vacuum lines, and FI Harness. It runs better than I expected but not good enough.

It idles too fast (1300 / 1400 RPM) considering throttle valve bypass screw is all the way in. Also, it runs lean (using WB A/F meter). I have set the mixture adjustment on the ECU full CW to get mixture around 13.7:1. I think I have covered all the common vacuum leak issues described in other threads. Any suggestions appreciated. I have two specific questions below.


1) Is my ECU P/N correct? The base P/N is correct but not sure what the 090 suffix means.

2) With the throttle valve bypass screw turned in full CW there is still vacuum getting past the screw. Does anybody know if that is normal ? I can put my finger over the port and feel vacuum. Maybe by design it is not meant to provide positive shut off but I don't have enough experience to say one way or the other.

Thx

[Montreal914]

You need to make sure everything is set properly such as dwell, timing, valve adjustment, vacuum hose connected to the right location, etc.

The knob on the ECU only adjusts the idle mixture. The throttle position switch sends the signal to the ECU that you actually are at idle. You need to verify that it is properly adjusted.

Everything you want to know on the D-Jet FI (at least a very good portion of it) is on this website:

http://members.rennlist.com/pbanders/index.html

I'm sure others will chime in.

Good luck and keep us posted (IMG:style_emoticons/default/beerchug.gif)

[Dave_Darling]

It's normal for air to still get through the bypass passage with the screw all the way in.

Your timing may be over advanced. But more likely, you still have a vacuum leak somewhere.

--DD

[luskesq]

I had a slightly high idle issue with my 1.7 (1200 rpm minimum) and eventually determined that my TPS wasn't adjusted properly.

Keith

[ggress]

Thanks for the input !!!

I am familiar with the B Anders site. Also, the J Bowlsby site and products. We are lucky to have some of these guys who have contributed so much.

Dwell, timing, and TPS are adjusted (checked multiple times). Verified that mixture selector on ECU changes A/F mixture with throttle valve closed. Verified vacuum lines are in proper locations using diagram from trusted site.

I have spent hours trying to locate a vacuum leak but have not discovered a significant culprit. MPS holds vacuum. For diagnostic purposes I plugged AAV connection at manifold /plenum and plugged decal valve connections.

Since the last post I did discover that the vacuum retard unit on distributor has a very small leak that can be detected with a vacuum pump. Also, valves are noisy for sure.

I will resolve vacuum retard leak and adjust valves next.

Thx

[JawjaPorsche]

Chasing a vacuum leak is a pain. Have you replaced your intake gaskets?

http://www.pelicanparts.com/catalog/SuperC...T_pg2.htm#item8

[era vulgaris]

I'm in the same boat as you, except I've got a 1.7 Djet and my idle won't go below 1200.
I think my issue has to do with the PCV, however I don't think that'll be a problem for you as I believe yours is routed to the air cleaner.

Have you checked your intake runner boots, intake manifold gasket, throttle body gasket, oil filler base gasket, cold start valve gasket, injector seals, and that you have the correct injectors?

Another forum member pointed out to me that his high idle was caused by one of his injectors being installed accidentally slightly at an angle. Even though his injector seals were new, the injector not being dead on straight allowed air to get past the new seal. Could be something to check.

[JeffBowlsby]

Nice to see you here Gary!

Here is one method of checking for leaks - from one of the Bosch manuals.

[Spoke]

You can locate vacuum leaks pretty easy with carb cleaner. Spray on hoses and all connections and listen for a change in idle.

Also make sure your AAR is closing remove the hose from the AAR to the air cleaner and plug it with your finger. It should be closed when the engine is warm.

[worn]

You can locate vacuum leaks pretty easy with carb cleaner. Spray on hoses and all connections and listen for a change in idle.

Also make sure your AAR is closing remove the hose from the AAR to the air cleaner and plug it with your finger. It should be closed when the engine is warm.

A definitive method is using a smoke machine to push smoke into a sealed intake system. Worked like a charm with the CIS system for my 911 -sure enough I had a failed diaphragm that let vacuum in, and of course, smoke out. I think there was something about this last week at the bird site.

[ggress]

I agree, it has to be a vacuum leak /s of some kind. I have ruled out the common leak sources mentions. I think there are a couple small leak sources rather than one obvious one. Going to try and find a smoke machine to confirm item 2 below.


1) After inspecting my TPS adjustment multiple times I found that I was over adjusting it in order to get the switch to operate properly. As a result the stop in the TPS switch was holding the throttle valve slightly open. The throttle valve shaft is worn (wobbles) this caused me to over adjust TPS to get proper function. I removed the TPS and jumped the switch so the throttle valve would be in a closed at idle. It helped but isn't the silver bullet. I plan to get the throttle valve rebuilt. Recommendations ?

2) This one has me scratching my head. Is it possible ? It looks like the manifold box / plenum is leaking where those hollow standoffs are brazed in. Has anybody seen this before ?

Thx

[ChrisFoley]

2) This one has me scratching my head. Is it possible ? It looks like the manifold box / plenum is leaking where those hollow standoffs are brazed in. Has anybody seen this before ?

Thx

I've seen 2 liter plenums cracked on the bottom - where its difficult to find the leak.

[914_teener]

You can take out the plenum and use a eak penetrant to check for cracks.

[boxsterfan]

Change your intake runner boots, intake manifold gaskets and/or fuel injector -ring seals?

[boxsterfan]

Change your intake runner boots, intake manifold gaskets and/or fuel injector -ring seals?

[ggress]

Everything is new, injectors / seals, FI harness, and every seal on the intake system. Also, as I stated before I eliminated the AAV and decel valve by disabling (plugged at manifold /plenum).

I have narrowed it down to two items for now. Throttle body leaks, will fixed but not the primary cause. See picture below; I may have found the culprit.