low revs on cold idle

Hello All,

I recently purchased a 2001 K11 Micra. Everything appears to be OK except for low engine speed on cold idle (idle when warm is fine - with higher revs than when cold). When moving the car whilst cold the engine almost stalls each time the clutch is pressed with no throttle but the revs pick up just before the engine dies.

The car has recently had a new throttle body fitted - Bosch type so no waxstat and no idle adjustment screw (which wouldn't be any use anyway as idle when warm is at the correct rpm).

I have checked the coolant temp sensor for the ECU and it is working normally (measures approximately 2.5k ohm at 20C and 450 ohm at 80C) also it is getting the correct 5V supply at the connector.

I'm beginning to suspect that the idle adjust valve is to blame but I don't know how to go about checking it's operation. Also I would have thought that it was the IAV that is kicking in and increasing the revs just before the engine dies each time that I change gear whilst the engine is cold. The IAV itself came with the new replacement throttle body.

The plugs are the correct Bosch type and were replaced about 2000 miles ago. I replaced a very old fuel filter yesterday but it made no difference to this problem.

There are no warning lights illuminated on the dash.

Any suggestions as to what I should try next would be appreciated.
 
OP
OP
C
Umm ok then, lets try 2 other questions and see if anyone can help with these.

Firstly does anyone know if the following procedure works for adjusting the base idle on facelift K11’s (I’ve only seen it identified as working for 1993 – 2000 models)?

1. Start engine run at 1k rpm until warm
2. Run engine at 2k for 2 minutes
3. Race engine 2 or 3 times under no load
4. Run engine for 1 min at idle speed
5. Turn off engine and disconnect Throttle Position Sensor (TPS)
6. Start engine
7. Race engine at 2k-3k 2 or 3 times under no load then run at idle speed
8. Check timing with a timing light – for Micra = 15º +/- 2º BTDC
9. Check idle speed
MT 650 +/- 50
AT 700 +/- 50
IF IDLE SPEED NOT WITHIN SPEC
9a. Race engine 2k to 3K 2 or 3 times
9b. Adjust idle speed by turning idle speed screw
10. Turn off engine and connect TPS
11. Start engine
12. Race engine 2-3k 2 or 3 times
13. Run at idle speed
14. Check idle speed
MT 650 +/- 50
AT 700 +/- 50

I know that I can’t do step 9b as there is no idle speed screw on the Bosch throttle body but I believe that I can get a similar effect by rotating the body of the Idle Adjust Valve clockwise a little.

Second question. Does anyone know what the resistance should be between the terminals of the Idle Adjust Valve on the Bosch throttle body? I have found information on this forum about the values for the idle adjust valve on the previous Jecs type throttle body being 50-100 ohms between pins 2 to 3 and 3 to 4. The valve on the Bosch throttle body only has 3 pins and mine measures 14.5 ohms between pins 1 to 2 and 2 to 3 and I have no idea as to if this is anything near the correct value.

Many thanks.
 
OP
OP
C
Thanks for the link R-REG-SR but it's not much use to me.

Looks like the issue there was that the revs were being kept high over the entire temperature range due to a sticking waxstat and that removing the waxstat resolved the problem. Mine has the Bosch throttle body - so no waxstat to begin with.

If anything mine is working the opposite way around to expected - low revs when cold (less than 500 I think - no rev counter so best estimate) then increasing to over 1000rpm once warmed up. It's behaving almost as though the idle adjust valve has been wired up backwards.

I don't understand what is causing the low revs when cold - the engine should be running in an open loop configuration with the idle valve held open and the engine spinning at about 1200rpm. I'm stuck trying to figure out what to change to get it to do this.

Does anyone know if the ECU on the 2000 - 2003 k11's need to learn the idle air volume when the throttle bady is changed?
 

frank

Club Member
there,s very little expertise on here regarding the coilpack engines crispy, there may be some info on the ilexa forum ?, or the QG setups are very similar
 

pollyp

Club Member
Thanks for the link R-REG-SR but it's not much use to me.

Looks like the issue there was that the revs were being kept high over the entire temperature range due to a sticking waxstat and that removing the waxstat resolved the problem. Mine has the Bosch throttle body - so no waxstat to begin with.

If anything mine is working the opposite way around to expected - low revs when cold (less than 500 I think - no rev counter so best estimate) then increasing to over 1000rpm once warmed up. It's behaving almost as though the idle adjust valve has been wired up backwards.

I don't understand what is causing the low revs when cold - the engine should be running in an open loop configuration with the idle valve held open and the engine spinning at about 1200rpm. I'm stuck trying to figure out what to change to get it to do this.

Does anyone know if the ECU on the 2000 - 2003 k11's need to learn the idle air volume when the throttle bady is changed?

my 1993 slx used to have the same slow cold idle and fast warm idle when i first got her, even after removing the seized waxstat. fixed it after adjusting the IAV by setting the IAV to 0 value in datascan active tests (or any consult diagnostic progs) then turned the IAV motor relative to the IAV body till the opening just blocks out light. tightened screws, reassembled, adjust warm idle speed screw, checked timing and all worked fine again.
 
OP
OP
C
I’m afraid that this is going to turn into a cautionary tale regarding cheap aftermarket replacement throttle bodies.

As the weather got colder last week my problem with the low revs whilst the engine was cold got progressively worse. By Saturday morning (nice and icy) my Micra was cutting out every time I let the engine idle. This is particularly interesting as you lose both the power steering and the vacuum for the brake servo when this happens – so if the engine dies whilst you are braking on the approach to a roundabout on an icy dual carriageway things can get very scary very quickly.

Managed to get my car to a local garage where we starting swapping bits over between a known good Micra of the same age and my own car.

Turns out that the idle adjust valve on my car (which is pretty much new having come with the replacement throttle body assembly that had been fitted by a previous owner) is completely non functional. As soon as the valve from the other Micra went onto my car the engine idled just as it should from cold.

My car also has a recurring problem with the engine warning light coming on indicating a P0171 – system too lean, bank 1 fault. So we had a look at the ECU and the live data with the engine running – everything appeared to be fine with both lambda sensors switching as they should (looks as though the front lambda sensor was recently replaced by a prior owner too). The only thing that we found odd was that the long term fuel trim was very high. Suspicions are now that the MAF in this replacement throttle body is giving faulty readings.

If the MAF sensor is consistently reading too low then the ECU will put too little fuel into the mixture based on the MAF sensor data. The front lambda sensor detects the weak mixture and the ECU subsequently compensates by adding extra fuel to rich up the mix. If this continues over time you end up with a high long term fuel trim value as the ECU basically gets used to having to offset the mixture based for the poor MAF data.

We think that this is what has been going on with my Micra. Most of the time the ECU can compensate for the poor data from the MAF but on some occasions the output from the MAF is so far out that the system can not alter the fuel trim enough and I end up with the P0171 fault popping up again.

So this replacement throttle body assembly appears to be s**t with the idle adjust valve known to be faulty and the MAF sensor suspected of being faulty. Unfortunately there are no manufacturer markings on the throttle body or on any of the sensors that are attached to it – so I can’t warn you about the particular brand. One thing that I do know for sure is that it is definitely NOT a Bosch part.

The mesh on top of this aftermarket throttle body is much finer than that on the original Bosch unit and the connector for the MAF sensor is red (instead of the originals black).

I’m stuck searching around salvage yards now trying to get my hands on a used Bosch unit (already have a can of carb cleaner at the ready). There is no way that I can afford a new part from Nissan – and the cheapest that I can find a new Bosch part for on the net is £551.94 from Euro Car Parts! I also can’t use the services of BBA Reman or ECU testing.com to get a reconditioned part as they both stipulate that they sell their units on an exchange basis and that your old throttle body must be returned to them in serviceable condition (something that I doubt that mine is). Having no exchange unit to hand ends up bumping up the price of a reconditioned part to something approaching £300.

So there you have it people – the end of my sad little tale. The moral being don’t always buy the cheapest part you can find as it may end up costing you more to put right than if you had simply spent a little extra getting the right part for the job in the first place.
 
OP
OP
C
I though that it might be useful (for someone one day maybe?) if I was to put some information up regarding resistance measurements taken from the Bosch throttle body that I picked up from a salvage yard yesterday and some taken from the suspect aftermarket throttle body that was fitted onto my Micra by the previous owner.

Bosch Throttle Body 0280750051

AFM/MAF 0280218040
Resistance measurements – all taken at room temperature with throttle body removed from car
I couldn’t find any number markings on the pins themselves so I have called the pin lowest to the bottom of the throttle body pin 1 and pin 5 is the one closest to the top.
1-2 = 341k
1-3 = 337k
1-4 = >40M
1-5 = 339k
2-3 = 4.49k
2-4 = >40M
2-5 = 6.7k
3-4 = >40M
3-5 = 2.2k
4-5 = 26.7M

Throttle Position Sensor (TPS) 0280122014
Throttle fully closed
1-2 = 2.18k
1-3 = 2.84k
2-3 = 0.99k

Throttle wide open
1-2 = 2.18k
1-3 = 1.10k
2-3 = 2.72k

Idle Adjust Control Valve (IACV/ICV) 0280140583
1-2 = 17.6
1-3 = 33.3
2-3 = 15.7

For the aftermarket copy throttle body the resistance measurements (taken under the same conditions) are as follows:

Unknown manufacturer aftermarket throttle body – No part number on casting. The machining of the casting is reasonable but the machined areas show that the casting itself contains a lot of small voids.

The top of the throttle body contains the same plastic grid and wire mesh parts as the original Bosch unit but assembled in a different order. The Bosch unit is assembled in this order (from bottom to top) wire mesh, spring washer, coarse plastic grid whereas the aftermarket copy is assembled in the order of spring washer, coarse plastic grid with the wire mesh at the top.

AFM/MAF – No part number
This is the only part that I could find a manufacturers name on – Sacer http://www.sacer.com.cn/doce/product-detail-11.html . The entire plastic moulding on this part is red in colour.
Now to be fair to Sacer, the Bosch part number for the original AFM does not appear on their list of compatible parts for their own AFM. Looks like someone might be assembling throttle bodies with the wrong parts.
Again no pin numbers on moulding so I have taken pin 1 as the one at the bottom of the connector and pin 5 is the one at the top.
1-2 = 61.3k
1-3 = 33.4k
1-4 = 37M
1-5 = 36k
2-3 = 28k
2-4 = 27M not steady
2-5 = 30.6k
3-4 = 24M not steady
3-5 = 2.52k
4-5 = 5.6M to 1.5k not steady

Throttle Position Sensor (TPS) - No part number
Throttle fully closed
1-2 = 2.67k
1-3 = 3.69k
2-3 = 1.39k

Throttle wide open
1-2 = 2.67k
1-3 = 1.47k
2-3 = 3.52k

Idle Adjust Control Valve (IACV/ICV) – No part number and known to be faulty
1-2 = 14.5
1-3 = 28.3
2-3 = 14.3
 
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