m20 bouncing and high idle/hesitation problems

[itsonlygeorge]

Symptoms trying to address/diagnose:

Bouncing idle on start.
High Idle when warm, 1200-1500 rpm steady. Rpms drop if pull oil dipstick.
Seems to be running rich(?) as there is a strong gasoline smell from exhaust.
When clutching in or coming to stop rpms drop at slow rate.

Does anyone know the resistance values for the 4 temperature sensors/switch on the m20 eta engine? I am trying to diagnose a rough idle/high idle when warm problem.

I know there is a Temp Sensor for the ECU, a Temp Sensor for the Gauge, a Temperature Time Switch, and another Temperature switch. I am trying to diagnose these items properly.

I checked the Temp Sensor and the resistance values were off, so I ordered a new one from bavauto pn 0 280 130 026 Bosch Fuel Injection Temperature Sensor (Blue Electrical Connector).

The Time Temperature switch is significantly more expensive and I am not sure how to test that one.



12 ENGINE COOLANT TEMP SENSOR
13 Temperature sensor, water
15 TEMPERATURE SWITCH
16 TEMPERATURE-TIME SWITCH

[itsonlygeorge]

So I did some more digging and found a few diagrams for the Temp Sensor and Thermo-Time switch.

Temperature_Sensor_NTC_M12_Datasheet
Coolant Sensor (ECU)
-18c 12000
18c 2315
94c 250

-15c 12002
30c 1707
100c 187

Also found these on the forum.

And these.

Model: 325, 325e, 325es
Connector color: white

Temperature Resistance
14+-4 F (-10+-1 C) 7000-11600 ohms
68+-2 F (20+-1 C) 2100-2900 ohms
176+-2 F (80+-1 C) 270-400 ohms

Model: 325i, 325is
Connector color: blue

Temperature Resistance
14+-4 F (-10+-1 C) 8200-10500 ohms
68+-2 F (20+-1 C) 2200-2700 ohms
176+-2 F (80+-1 C) 300-360ohms

Time-Temperature Switch
I got these off a thread for a CSI, but I assume they are pretty close in design.
http://www.bimmerforums.com/forum/sh...switch-issues)

Time-temperature Switch Resistance Values

Time-Temperature Switch Internal Construction

Cold Start / Time-Temperature switch operation

[Andy.B]

I highly recommend obtaining the Bentley manual (either a hard copy or online).
The fuel system section gives a thorough overview of operation, testing, and diagnosis of the sensors, and their role in the system.

[itsonlygeorge]

I followed the Bentley procedure and tested the Cold-Start Valve and thermo-time switch, and retested the Coolant Temp Sensor.

Results: (@ 28 F ambient)

Cold-Start Valve fires for ~6 seconds and is clean.

Thermo-Time switch:
G+Frame/ground (engine block): 36.7 ohms
W+Frame/ground (engine block): 0.01 ohms
G+W : 36.7 ohms

Coolant Temp Sensor (two prong white top): 6000 ohms (cold)
Coolant Temp Sensor (hot, needle at mid gauge): 2900 ohms

Symptoms trying to address/diagnose:

Bouncing idle on start.
High Idle when warm, 1200-1500 rpm steady. Rpms drop if pull oil dipstick.
Seems to be running rich(?) as there is a strong gasoline smell from exhaust.
When clutching in or coming to stop rpms drop at slow rate.

[LateFan]

We kind of went through this as well.

I vote:

Vacuum leaks / cracked hoses / intake boot / old valve cover gasket / etc. - have a smoke test done.

Change the temp sensors, even just to eliminate the possibilities. Some just go to the dash cluster, some to the computer, some affect cold idle.

Idle control valve / idle control module (in the glove box).

Test fuel pressure at the rail.

Check O2 sensor as well. We had a small crack in a down pipe just upstream from the O2 - made all kinds of problems.

Search for JLevie posts on diagnostic steps, as well as Bentley.

[itsonlygeorge]

I changed the temperature sensor and reset the ecu and not much changed. New sensor reads 290 ohms hot.

The car will idle at ~750 - 900 rpm until it warms up. Then the rpms will shoot up to 1200-1500 and stay there.

When I drove it an the idle is at 750 it stutters and there is a loss of power up until 3000 rpm. Above 3000 rpms it pulls fine. Once it's warmed up and idling at 1500 rpms there is no stuttering but the rpms drop slowly when shifting.

I left the car idling while I went to an atm and the rpms dropped down to 750 on their own and it drove like crap until it decided to idle high. Something is not right, and it doesn't point to a vacuum leak.

[digger]

vacuum leaks, ICV, TPS

[moatilliatta]

You check basics?

Vac leak, Spark plug cond, Fuel pressure.

Maybe getting in deep, but you haven't even skimmed the waters.

[itsonlygeorge]

Spark plugs are fine, checked a few days ago when it was warmer outside. Need to get a smoke test done, hoses have been replaced within 2 years.


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[itsonlygeorge]

So I decided to check the O2 sensor and PO's build thread and I learned that the o2 sensor used was the mustang sensor and was not positioned in an ideal location on the exhaust. It may have gunked up or thw wiring may have gone bad over the winter. (This is Maine and the winters suck)

I unplugged the O2 sensor and sure enough the hesitation/surging went away. I tried letting the engine cool down and replugged the 02 sensor and the same symptoms came back. I've been running it for a week w/o the o2 sensor and its been fine so far. I will need to clean/replace the o2 sensor in a few weeks when its warm out and I can get the car up. I did adjust the ICV (cranked it down to where I remember it being before I messed with it) and that has helped the high idle somewhat (but the bouncing idle is back when the engine is cold)

I still plan to get a smoke test/leak down test done as well as brakes/rotors, spark plugs, timing belt, h20 pump, valve adjustment/cover gasket, and potentially oil pan gasket if I am able to find an engine lift. Oh and i need to replace the gas tank as well since a shop here damaged it while doing an inspection.