84 sentra - trying to figure out problem !

[mickey-d]

Hi,

  New plugs, wires, rotor, cap, o2 sensor, timing set to spec,cleaned carb, compression test great, rechecked everything twice.

Fires right up, but will sometimes idle fine, then will speed up by itself, then idle way down, straighten out, then do it again, driving me crazy!

  Any help would be great

[ggzilla]

1. Unplug the carb wiring connector and plug it back in

 

2. Check the float level

 

3. Check the automatic choke. If it needs adjusting drill out the rivets and replace with screws. See Choke

 

4. Search for vacuum leaks

[datzenmike]

O₂ sensor? So this must be a feedback carb then. One of the things likely on this carb is a throttle valve switch. This switch is set to close at idle and open at any other position so the ECU knows you are no longer idling. May need adjusting or wire loose. Wiggle the electrical plug and pinch wires at back of carb and see if problem comes and goes. 

[mickey-d]

Thanks for the link, and for both of your advice.  Its 109 out there right now, so I'll research your advice and try it out in the morning.

Have to locate the throttle valve switch, and read up on the link.

Just in case..its a hitachi DFE 2832  2barrel....Are they fairly easy to rebuild ? I'm good taking things apart and putting back together, but haven't tried a carb.

Thanks

[ggzilla]

It doesn't need rebuilding

[mickey-d]

Yea, I have the feedback, electronically controlled carburetor ... No rivets or automatic choke,It has a Idle speed control actuator and lots of sensors and switches, all controlled by the computer.  The butterfly is barely opening  Even when up to op temp...trying to figure out how thats controlled..which sensor sends to computer to control this?   or is computer messed up?

 

 Checked all connections and plugs, vacuum lines, and wires. I found some test I can try in the manual...it also has a air-fuel ratio solenoid inside the carb that may be causing problem.

[ggzilla]

Very unlike the computer is messed up.

 

If a sensor is bad the code can be read, per the manual.

 

More likely the IAC is plugged or otherwise not working.

[ggzilla]

Got photos?

 

How's the fuel level look? Is it right on dot within 1 mm?

[mickey-d]

Float is right on the money, I'm going to test the senors and switches according to book.

The IAC is actually that big -( idle speed control actuator,) with five vacuum lines running to it. I'll be checking that too...

tomorrow morning, its up to 106 now.

Not sure on picture, doesn't give you option to browse photos

Thanks

[ggzilla]

Yes that's right.

Put your photo on some photo web site. Most of us use Photobucket. Then in your reply, link to the photo.

[mickey-d]

While I've been researching articles about the vcm feedback carb system on my 84 sentra, I came across this description and it

seems to fit, it was called  ( The Hopeless Chokeless System )

[datzenmike]

Some later Z24 720s had them. The wiring to the plug is too short and gets tugged on when moving. The wires break inside the insulation and cause all kinds of ramdom problems. 

[mickey-d]

Which wire do you mean ? The connector right on the VCM ?

Also, in your earlier post you mention a throttle valve switch ? not sure where or what that is