Water Temp Sensor??

I've had an ongoing issue with my car for about 3 years now.......
At cold start the engine will idle perfectly fine for about the first minute after a cold start-up, then with a blink of an eye it will idle down and kinda run rough for about 30 seconds, then with another blink of an eye it idles back up and idles perfect for the remainder of the day. It's like turning on and off a light switch. It did this with my old motor, and also my new motor. It is consistant with every cold crank.....and if the motor is warm it doesn't do it after start-up. It also did it with my old water temp sensor and also with a new temp sensor.
I discovered yesterday if I cold crank the car with the water temp sensor plug disconnected it doesn't do it.
The car does idle a little higher when I unplug it, and idles lower when I plug it back on......which is normal, and to my knowledge is working like it should.
I think I got it narrowed down somehow related to the temp sensor or the ecu wiring to it. Anyone know where the wires go leaving the temp sensor? Do they go directly to the ecu?
Could the ecu itself be faulty?
Any help would be great

Don't these cars have some kind of IAC motor? I know it's a long shot, but my T/A has an IAC underneath the throttle body that controls the cold engine high idle type stuff...

It has a IAA unit

Keith my 85 Turbo does the exact same thing except that it also has a rich bog at first cold start. Both problems go away if the temp sensor is disconneted even though the sensor is new also.

Interesting...........any ideas? Mine smells a little rich during this time as well.

I've been trying to figure this out for a while now. At one point I tried the tests in the FSM on checking the resistance that the water temp sensor gives out by checking the values at the sensor and at the ECU plugs. I got the same values so that should mean the wiring is ok. My new theory is that maybe the oxygen sensor heater element isn't functioning due to some wiring or ECU problem or something. I'll need to try the test in the FSM that talks about this but it's the only other thing I can think of at the moment because if you disconnect the water temp sensor the computer ignores the 02 sensor based on what i've seen.

Can anyone post a pic and show me where the temp sensor is located?

Can anyone post a pic and show me where the temp sensor is located?
What engine do you have?

ca18et, sorry...

Sorry......no pic, but it's located on top of the intake manifold right behind the thermostat housing. It screws into the intake mani, and has a 2 wire connector plugged onto the top of it and held on with a "U" shaped clip.

Hey Alan.......I was browsing through the FSM tonight, and found a section about the O2 sensor and heater control.
It says.........
CAS, AFM, and Water Temp Sensor goes to the ECU, then it relays the info from the 3 sensors to the O2 senor.
Then it says........"If engine speed is less than 2,800 rpm, and the water temp is more than 50 degrees the O2 sensor heater is on"
"If engine is more than 2,800 and water temp is less than 50 degrees O2 heater is off"

So at cold start-up the O2 sensor heater shouldn't be activated until the water is 50 degrees.
Looking at it this way....I don't think this our problem.....since the heater shouldn't be on at cold start-up.
Maybe the problem is the heater is coming on when the water temp is less than 50 degrees???

My CA20E did similar crap,
It runs rich every time u start it.
If u shut it off then start it within 5 or so seconds, it will cgug for a second or to then pik up reva agian. u?

Well, my Fuel pump has gone. Mechanic rekons that the chuggn bit is the fuel pump not pushn the fuel for a sec. And it will slowly get worse.

Gettn my fuel pump replaced tomorrow. , will tell ya's if this rich stuff and chuggn stops.

Good info there Keith. Yes after more thought it may not be the 02 sensor after all. I'm thinking it may just be something with the water temp sensor circuit that isn't right. Cause i remember disconnecting the 02 sensor with the water temp still hooked up and it still bogged. Seems to be directly related to the water temp sensor circuit in some way. I've also been thinking about how there are like 3 different water temp sensors for the CA18ET engine. I wonder how much different they are and if maybe somehow the ones we have aren't right or maybe the wiring changes resistance when it gets old? Also what if someone switched to a later ECU in our cars before we owned them due to failure or something and the new water temp sensor isn't the correct one for that ECU as they made changes in those. Any more ideas? Something screwy in the ECU? Whatever it is if we ever figure this out it will need to be a sticky.

There should be a procedure for checking the resistance, etc. for the water temp circuit at both the harness side and the ECU side in the service manual. You should run through those procedures with a multi meter and see if you are getting the correct readings. That would be the best way to go about it.

My old temp sensor I bought was from Nissan about 4-5 years ago. I just can't remember if it was already doing this before I installed it......but it was doing it before the old motor croaked. When I put in the new motor a few months ago the new temp sensor I got was from NAPA, and the bottom of it looked a little different than the Nissan one and also is stamped with 140 degrees on the copper bottom.....but any case it does the excact same thing now with the new motor. So I don't think it would be the temp sensor itself. Also, I don't think it would be that someone swapped out the ecu before I got it, because I have owned the car since 1988...and the problem didn't start till around 1999-2000.
Also I replaced the ecu connector that connects on the temp sensor with a new one......so if it's the wiring....it must be further up stream. Any idea where the 2 wires go? Do they both go to the ecu? I'm wondering if it just might be a bad ecu??
But as Spooled suggested I need to check the resistance at the ecu. I've done it at the temp sensor and it was within specs.

Yeah i checked mine once, the value at the sensor itself and the value at the wiring to the ECU and it was the same resistance value. That should mean that the wiring is fine and i'm not sure what else it could be. What about the vacuum solenoid thing for the Fuel Pressure regulater? T.V.V. valve?

My TVV is also new with the new motor.
Question though......the 2 nipples on the TVV.....on mine one hose goes to the carbon canister, and the other goes to the BPT/EGR valve/nipple under the tb. Is one suppose to go to the fuel regulator? Because my fuel regulator doesn't.....I got it plugged onto the little nipple right behind the tb on the intake manifold.....right accross from the fuel regulator. Is this wrong??? Hmmmm wonder if this is my problem......cuz I replaced all the vac lines around the same time a few years back.

My TVV is also new with the new motor.
Question though......the 2 nipples on the TVV.....on mine one hose goes to the carbon canister, and the other goes to the BPT/EGR valve/nipple under the tb. Is one suppose to go to the fuel regulator? Because my fuel regulator doesn't.....I got it plugged onto the little nipple right behind the tb on the intake manifold.....right accross from the fuel regulator. Is this wrong??? Hmmmm wonder if this is my problem......cuz I replaced all the vac lines around the same time a few years back.

this is what i'm asking in my frp thread (that no one has been able to answer).

this is what i'm asking in my frp thread (that no one has been able to answer).
Well, after looking at the FSM for the CA18.....it looks like I have the FPR vac line plugged where it suppose to be....which is on the intake manifold right below the TPS.
As far as the TVV vac lines I need to re-do mine as there not the same as the FSM.
In the FSM it shows the bottom nipple on the TVV going to the carbon canister, and teeing off and going to the EGR and BPT valves.
On the upper nipple on the TVV it goes straight to nipple on the throttle body.
I don't think this will cure my problem......but who knows

i don't think the mk2 have a tvv... i have a mkI fsm and it shows the tvv plugged into the block coolant. the only tvv i have has one vacuum line in and 2 out...

i tried plugging the fpr directly to the manifold. it did give increased boost response but i had a high idle and maybe even some knocking at idle... (or detonation in the exhaust).

If you have the TVV it screws into the intake manifold right behind the water temp sensor on the CA18.....not sure on the CA20. Also the CA18 has 2 nipples, where the CA20 has 3 coming off the tvv.

i'll check again tonite, but i don't remember seeing anything like that on my MK2. in any case i'm probably going to have to go thru all the vacuum lines one by one as i'm almost certain that is what's causing my drivability problems.

Seems like Bart told me his '86 doesn't have the TVV....so your probably doesn't either.
BTW I was just checking out your car domain............do you still have the a/c dryer bottle on the car.....because on mine it's located right where you got the intercooler. Does your I/C fit in front of it?

ya my mk1.5 doesnt have that but my mk1 ca18et does..

i guess i need to dig up a mk2 fsm on ebay to get my hosing sorted out =( crap. if the guy who got the 88 fsm read this, please scan the vac hose diagram!!

i took out the ac condenser & dryer bottle (i bought the car with no compressor). not sure if you could squeeze my ic in there with the stock condenser and dryer. i think the ic fits it's getting the piping thru that would be hard. you'd probably have to to do a lot more cutting than i did (i did almost none) or route the hoses below or above.

Well.....got the vac lines straightened out to how it shows in the FSM......and to no surprise it didn't cure the problem. Oh well, back to square one!!

Yes this is quite the pesky problem. The day we figure this out is the day i'll be very very happy.

i think your temp sensor is ok. by disconnecting it it causes the ecu to make the mixture extra rich (and shut off the exhaust side plugs too, i think). if you cannot find a cure for your low idle situation you can wire the temp sensor to a switch and turn it off for the 30 seconds it takes to normalize. i did this for a while to cure a different running problem...

or get a ka tb and run high idle ALL the time =)

or get a ka tb and run high idle ALL the time =)
I've had a KA tb on for a couple of years now....and the problem exsisted before hand.
Also.....what I have the idle set to....doesn't seem to matter with this problem, because it will still do it no matter what.....for example, if I set the idle to 2000rpm, and crank the car cold, the rpms will still drop and run rough all of a sudden for about 30 seconds.....then clear up, and idle smooth and back to 2000.

hmmm, maybe your idle up solenoid is malfunctioning? do you notice if the car is rich during the rough idle period?

hmmm, maybe your idle up solenoid is malfunctioning? do you notice if the car is rich during the rough idle period?
It does smell a little rich.....but thats normal for a cold start-up. It smells a tad rich before, during and after the bog until the engine warms up some.
It does idle up when I turn on the headlights or a/c so I think the idle up solinoid is ok

Yeah mines the same way. I've even rigged the air regulator so that the cold idle speed is higher at just under 2000 rpm and it still does it. It's a rich condition but bringing in more air doesn't solve it as the MAF must compensate for it. Don't think it would be anything MAF related either as i've used the original and an 86 turbo MAF and no changes there either.

Yeah......my maf is only about 3 years old. Maybe I'll put the old original one on to see if it still does it......just for kicks.

ok, if you really want to test your water temp sensor you can intercept the signal and put in a potentiometer (variable resistor). water temp sensor is supposed to rise to 10k ohms or so (can't remember off hand) depending on the temp. you can fool with the resistance and see if that has any effect on your bog. it's not hard and if you get small spade connectors (or file a few down) you can plug directly into your sensor plugs (yes, i've done it). you can get a 0-50K pot for a few bucks at radio shack.

note: unplugging the temp sensor has an entirely different ecu routine than fooling the car into thinking it's hot/cold.

Hey alan............just discovered today that when these symptoms begin the timing retards about 5 degrees...then when it clears up, the timing advances back to normal.
Any ideas???

Hmmmm how did you find this out? Were you playing around with a timing light and noticed this? Very interesting. I'm not sure what that means though. I'm sure it's not the crank sensor because i've had more than 1 of those and it didn't make a difference. Also my Detonation sensor is disconnected so it can't be that either. Gotta be something in the ECU or something related to the timing system. Anyone got any ideas for what we should be looking for?

yeah...I was just screwing around and decided to check the timing when I first cranked the car...and the timing was right, then when the problem kicked in...I checked it again, and noticed it was retarded 5 degrees. So I decided to keep the trigger pulled on the timing light and pointed at the crank and waited to see what it would do once it came out of rough idle........and sure enough the same point it came out of rough idle, the timing advanced back 5 degrees to it normal spot.....which I saw with the timing light.
Try it on yours and see if it does the same thing.
I'm starting to think it just might be a bad ECU??

mine does the same thing with the timing....

Yes i'll have to go out and try that to see if the timing does the same thing. Based on what it sounds like and acts like that seems to make sense. The engines tone changes when the bog starts and it does sound a lot like the timing is retarding and then when it goes back to normal it sounds fine again and runs fine again. I think we may be onto something here, we just need to find out what is the cause of the timing change now.

Oh......another thing I notice now since it's cold here.......when I first crank it in the morning it takes about 2 minutes to go into a bog, and about another 2 minutes to come of out it.....whereas in the summer time it went into a bog about 30 seconds after starting, and came out about 45 secs later.

Yeah mine is the exact same way with the colder weather. It's pretty annoying and really the only thing I dislike about my S12. We really need to figure this out. We do know that disconecting the water temp sensor cures it. Does the water temp sensor circuit affect timing at all or just fueling?