325es surging at idle/ driving when motor cold, getting horrible MPG - BMW Forum - BimmerWerkz.com
3-Series (E21, E30) Chat relating to the BMW 3-Series from 1975-1983 and 1984-1991 line. Specific models: BMW 315, BMW 316, BMW 318, BMW 318i, BMW 320/4, BMW 320i, BMW 320/6, BMW 323i, BMW 320i. E30 Family models include: BMW 325e, BMW 325i, BMW 325is, BMW 325ix.

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#1 (permalink) Old 01-01-2007, 07:16 PM
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325es surging at idle/ driving when motor cold, getting horrible MPG

i was not having this problem before, it started about 2 months ago when the weather started getting cooler. it always surged at idle, but now its doing it while its driving before the engine warms up. also i getting horrible gas mileage. went from about 28-29 mpg down to like 20-21. just wonderd if they were related. i took it to a shop and they said replace the idle control valve. (a few others on the forum said so too in an earlier post) im just wondering if that will fix my mileage problem too.

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#2 (permalink) Old 01-01-2007, 09:22 PM
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i just cleaned my idle control valve for free just remove the idle valve and take a can of brake cleaner and hose it out, usually does the trick and saves you a chunk of cash

Kyle Sutherland

1995 BMW 540i/6:
The Calypso Beast Vid 0-70ish
1987 BMW 325es: Face & Butt Lifted/M50tu Swapped*Sold*
1985 VW Scirocco: Too many mods, money pit*Sold*
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#3 (permalink) Old 01-01-2007, 11:13 PM
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Quote:
Originally Posted by whitey_E30
i was not having this problem before, it started about 2 months ago when the weather started getting cooler. it always surged at idle, but now its doing it while its driving before the engine warms up. also i getting horrible gas mileage. went from about 28-29 mpg down to like 20-21. just wonderd if they were related. i took it to a shop and they said replace the idle control valve. (a few others on the forum said so too in an earlier post) im just wondering if that will fix my mileage problem too.
Like I said before the #1 cause of a screwed up idle and bad mpg is a faulty coolant temp sensor.
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#4 (permalink) Old 01-02-2007, 12:38 PM
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went and got a coolant temp sensor. i thought it mounted right up on the drivers side of the radiator but im not sure. it looks like there are 2 sensors thereand neither of them have connectors like the new sensor i got. maybe he gave me wrong part? the one i just picked up it the pic on the car hood. the one with the nice puke yellow plug. used:
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#5 (permalink) Old 01-02-2007, 01:22 PM
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i think i found where the sensor could go but im not sure. theres only about 12 different places. help?

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#6 (permalink) Old 01-02-2007, 02:51 PM
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according to the bentley manual which every E30 owner should have its right there...



BTW love the avatar

Kyle Sutherland

1995 BMW 540i/6:
The Calypso Beast Vid 0-70ish
1987 BMW 325es: Face & Butt Lifted/M50tu Swapped*Sold*
1985 VW Scirocco: Too many mods, money pit*Sold*
E34 Plate Filler Wanted!
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#7 (permalink) Old 01-02-2007, 05:47 PM
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That is the coolant switch, that makes the car fast idle when cold. The yellow sensor is the correct one for the computer and idle module, it'll go right next to the #1 injector. You can get at it from the passenger side just under the air intake. There will be two sensors there, the one above it has one pin and that runs the gauge. The ones in the rad are the high and low speed fan switches.

P.S. The coolant switch is used in 87 and older cars with the idle control module, in 88 and up models the idle module is intergrated with the DME.

Last edited by Starmavin; 01-02-2007 at 05:53 PM.
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#8 (permalink) Old 01-02-2007, 06:02 PM
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wow i was lookin at the pic in the bentley backwards, you are correct sir, its on the cylinder head, coolant outlet next to the thermo switch

Kyle Sutherland

1995 BMW 540i/6:
The Calypso Beast Vid 0-70ish
1987 BMW 325es: Face & Butt Lifted/M50tu Swapped*Sold*
1985 VW Scirocco: Too many mods, money pit*Sold*
E34 Plate Filler Wanted!
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#9 (permalink) Old 01-04-2007, 09:38 AM
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so there is the coolant temp sensor and the thermo time switch, what are the differences and do they both contribute to bad mpg and erratic idle?
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#10 (permalink) Old 01-04-2007, 01:05 PM
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ones a sensor(just monitors temp) and one is a switch (sends a ground signal a certain temp) usually used for timing and idle control, but it is rarely the culprit because the only function it has is open or closed...closes below 86*F and open at about 118*F

idle valves get clogged which cause the surge, as i stated above, just take it off and hose it out with brake clean

Kyle Sutherland

1995 BMW 540i/6:
The Calypso Beast Vid 0-70ish
1987 BMW 325es: Face & Butt Lifted/M50tu Swapped*Sold*
1985 VW Scirocco: Too many mods, money pit*Sold*
E34 Plate Filler Wanted!
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#11 (permalink) Old 01-04-2007, 06:35 PM
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Quote:
Originally Posted by jfertita
so there is the coolant temp sensor and the thermo time switch, what are the differences and do they both contribute to bad mpg and erratic idle?
Ok, this should clear everything up. In all you have 6 temp sensors/switches on any 325 that is 87 and older. As mentioned before, the two in the radiator are for high and low auxiliary fan speeds.

The 4 in the motor found in and near the thermostat housing are as follows:

The thermo-time switch, this operates the cold start injector only, this is the larger one closest to the front of the motor.

Coolant temp switch is the next one back, is for cold warm up, this holds an open circuit until the cars coolant reaches the set temp then closes. gotKRAUT posted a pic pointing this one out.

Next one in has one pin and is for the gauge.

Then the last one is the coolant temp sensor, this is the most important sensor, it looks exactly like the sensor for the gauge but with two pins, this sends engine temp signal to both DME and idle control module.

Last edited by Starmavin; 01-04-2007 at 06:41 PM.
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#12 (permalink) Old 01-05-2007, 08:54 AM
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I got the coolant temp sensor in... but im still getting horrible gas milage and car still chugs before it warms up. so it didnt work. any more ideas.

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#13 (permalink) Old 01-05-2007, 05:43 PM
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When cold remove the cold start injector then plug the hole with your thumb or anything that won't get sucked in, then have someone start the car, see if and how it is sprays fuel, hold a cup up to the injector it should spray a fine mist for 3-4 seconds then stop. While the car is warm, shut it off and remove the cold start injector, plug the hole, then have someone start the car, see if it is sprays fuel again.
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#14 (permalink) Old 01-17-2007, 07:18 AM
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just replaced the ICV, and the car still is showing the same symptoms as before. erratic idle, poor fuel economy. i dont have much time to do work on it. is there anything else that is easily replacable that could possibly be the culprit??? it only does it when its cold. after driving for about 20 mins, it runs fine once it warms up while im crusing down the road.

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#15 (permalink) Old 01-17-2007, 08:07 AM
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You can try testing your thermo time switch if you havent done that yet, only other thing i would suggest is vacuum leaks or something with your fuel system
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