75 1.8 manual; Surging deceleration and wavering idle! - Page 2

Rover Roy · 8th December 2006, 18:01

Recieved the Haynes manual tonight. A quick read through left me disapointed in the lack of explanitry detail on Engine management but page 4A-2 (1.8) does mention several sensors roles.

I think M47Rman has hit the nail on the head with the indecision of ECU mapping. I have already swapped the idle air valve ( with a used unit) without a fix which tends to suggest a sensor problem influencing the Part/full map. Ive checked engine response with rear window demist, and A/C and idle responds OK. As I see it that leaves the Power Steering sensor. Any ideas how to check it????

Simon · 8th December 2006, 20:34

Not yet got my copy of Haynes manual (its an xmas prezzie, ya see) so this explanation is a bit of a stab in the dark...

If the power-steering sensor is malfunctioning then I would expect there to be a drop in engine revs at idle speed. The reason being the servos for the power steering require an awful lot of power (and I mean, an awful lot). If the ECU cannot compensate this power increase because the sensor is not telling it that you are turning the wheels then I would expect there to be a drop in idle speed when you turn the wheels.

As a way to check this, I say park, put car in neutral and leave all other loads off (ie, HRW, ATC etc all off) then listen to engine/look at rev counter while you turn the wheels (dry turning). If the engine speed noticiable drops then I would expect the power steering sensor could be faulty.

Of course, if this information is proved incorrect by a later post, then I do appologise

Rover Roy · 9th December 2006, 11:52

Checked the P/S sensor using the method Simon D suggested. Idle response was as it should be so all OK. This looks like a process of elimination, but how many sensors are there left to check???? I have almost convinced myself that the throttle position sensor could be the culprit as the surging seems to be only at light throttle use. Took a look under the bonnet this morning and quickly realized that doing any work on removing the throttle body was beyond the ability of me & my tiny tool kit. Decided to check what i thought was the MAS sensor(Mass Air sensor, i.e. Density) Haynes describe it at a MAP (Manifold Absolute pressure) !!!
Guess what, the sensor that is located downstream of the rocker cover vent tube was soaked in oil!!! A quick clean with meths (not from the drinks cabinet) was all it needed. A testdrive of about five miles at low throttle use just now showed no signs of the symptoms experienced all week.

I shall post again on this thread later in the week as an update.
Thanks to all rovers who contributed, amaising what can be achieved with group effort and alittle lateral thinking. (cheap too)

Simon · 9th December 2006, 20:11

Glad to hear eveything's ok now.

The throttle body can become soaked in oil residue from the blow-by from the pistons. Nothing to worry about unless oil is pouring out of the throttle body when you remove the upper part of the filter box.

As you say, cleaning the sensor with meth's or carb' cleaner shifts the muck and helps the engine out.

Let us know how things go!

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8th December 2006, 18:01	#11
Rover Roy Newbie Join Date: Dec 2006 Posts: 6 Thanks: 0 Thanked 0 Times in 0 Posts	Recieved the Haynes manual tonight. A quick read through left me disapointed in the lack of explanitry detail on Engine management but page 4A-2 (1.8) does mention several sensors roles. I think M47Rman has hit the nail on the head with the indecision of ECU mapping. I have already swapped the idle air valve ( with a used unit) without a fix which tends to suggest a sensor problem influencing the Part/full map. Ive checked engine response with rear window demist, and A/C and idle responds OK. As I see it that leaves the Power Steering sensor. Any ideas how to check it????

8th December 2006, 20:34	#12
Simon Banned - Join Date: Nov 2006 Location: - Posts: 10,318 Thanks: 0 Thanked 4 Times in 3 Posts	Not yet got my copy of Haynes manual (its an xmas prezzie, ya see) so this explanation is a bit of a stab in the dark... If the power-steering sensor is malfunctioning then I would expect there to be a drop in engine revs at idle speed. The reason being the servos for the power steering require an awful lot of power (and I mean, an awful lot). If the ECU cannot compensate this power increase because the sensor is not telling it that you are turning the wheels then I would expect there to be a drop in idle speed when you turn the wheels. As a way to check this, I say park, put car in neutral and leave all other loads off (ie, HRW, ATC etc all off) then listen to engine/look at rev counter while you turn the wheels (dry turning). If the engine speed noticiable drops then I would expect the power steering sensor could be faulty. Of course, if this information is proved incorrect by a later post, then I do appologise

9th December 2006, 11:52	#13
Rover Roy Newbie Join Date: Dec 2006 Posts: 6 Thanks: 0 Thanked 0 Times in 0 Posts	Checked the P/S sensor using the method Simon D suggested. Idle response was as it should be so all OK. This looks like a process of elimination, but how many sensors are there left to check???? I have almost convinced myself that the throttle position sensor could be the culprit as the surging seems to be only at light throttle use. Took a look under the bonnet this morning and quickly realized that doing any work on removing the throttle body was beyond the ability of me & my tiny tool kit. Decided to check what i thought was the MAS sensor(Mass Air sensor, i.e. Density) Haynes describe it at a MAP (Manifold Absolute pressure) !!! Guess what, the sensor that is located downstream of the rocker cover vent tube was soaked in oil!!! A quick clean with meths (not from the drinks cabinet) was all it needed. A testdrive of about five miles at low throttle use just now showed no signs of the symptoms experienced all week. I shall post again on this thread later in the week as an update. Thanks to all rovers who contributed, amaising what can be achieved with group effort and alittle lateral thinking. (cheap too)

9th December 2006, 20:11	#14
Simon Banned - Join Date: Nov 2006 Location: - Posts: 10,318 Thanks: 0 Thanked 4 Times in 3 Posts	Glad to hear eveything's ok now. The throttle body can become soaked in oil residue from the blow-by from the pistons. Nothing to worry about unless oil is pouring out of the throttle body when you remove the upper part of the filter box. As you say, cleaning the sensor with meth's or carb' cleaner shifts the muck and helps the engine out. Let us know how things go!