Idling RPMs get lower and lower

[TomFraser]

When my car is idling (MK3 N/A 5speed 1988)

it idles at about 1200 rpms fine then begins dropping. It goes low enough to almost cut out but then there is a click that sounds as if it is coming from the glovebox and it goes up to about 800 then begins going lower until it repeats, getting lower, faster each time.

I can keep it high enough if I give it a little gas or even just run the AC to use the engine...


Any ideas why these issues are happening? Are the common?


Thanks

EDIT: Posting vid on youtube... the only possible place the clicking could be coming from is the ecu i believe


VIDEO:

http://www.youtube.com/v/sAWvkeGK8ns around 1:40 is good example... if possible watch the whole thing so you can get an idea


Thanks for reading and taking the time

 

[TomFraser]

does it make sense that the clicking noise would be coming from the ECU?

 

[jetjock]

No.

 

[CRE]

Didn't listen to it... does the clicking sound like a relay?

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=22

 

[amichie]

There are no relays inside the ECU. It's all solid state.

 

[TomFraser]

Didn't listen to it... does the clicking sound like a relay?

http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=22

i honestly don't know...

the video has the clicking noise if that helps

 

[CRE]

There are no relays inside the ECU. It's all solid state.

Which, interestingly enough, may explain why I posted the information for the only relays I know of in that area. :icon_razz

 

[TomFraser]

One thing I should add is that it only does this occasionaly and randomly

sometimes when engine is hot, sometimes when cold, I cannot guess when or why it will occur

that is the main reason I took the video, so I could show mechanics... figured it wouldn't hurt to post here


Thanks for the help

 

[CRE]

Test the ISC (Idle Speed Controller), probably wouldn't hurt to dismantle it and clean it out. Inspect the ISC's harness. Test the TPS' IDL switch. That's where I'd start.

EDIT: I'd also test the ECUs coolant temp sensor.

 

[CyFi6]

i would pull down the glove box and look for any after market things in there/wiring first off

 

[TomFraser]

i would pull down the glove box and look for any after market things in there/wiring first off

The top one looks stock except those yellow and red wires.

The bottom is where I think the clicking is coming from


Thanks!

 

[TomFraser]

The top one looks stock except those yellow and red wires.

The bottom is where I think the clicking is coming from


Thanks!

I don't think the yellow wires and red wire are supposed to be there... the seem to be coming from the area behind the radio (might be hooked up to it)

 

[AJ'S 88NA]

You're right about the three wires they are not stock. Were are they going to on the other side of the firewall?

 

[TomFraser]

You're right about the three wires they are not stock. Were are they going to on the other side of the firewall?

They go to the battery and then go through the center of the car to the hatch (They probabbly connected to an amp) (RED = + , BOTH YELLOW = -)


Guess those aren't really important, gotta make sure they stay covered tho! (THEY ARE BARE RIGHT NOW)

EDIT: this must have had two different sets of subs at different times with different owners, as one used ground from the back, and another took it from the battery )

 

[jetjock]

Sounds as if your Circuit Opening Relay is dropping out. You'll need to pull the cover off to check it. Btw does the MIL come on during this? If so that would explain a lot.

Question for those who want to try: many cars have that hose on the blower motor. What's it purpose?

 

[CyFi6]

I could only imagine its for some type of cooling for the motor or for some kind of pressure difference... Teach me old wise one.