Volvo RWD 900 Forum

INDEX FOR 10/2025(CURRENT) INDEX FOR 3/2007 900 INDEX

[<<]  [>>]


THREADED THREADED EXPANDED FLAT PRINT ALL
MESSAGES IN THIS THREAD




  REPLY TO THIS MESSAGE Replies to this message will be emailed.    PRINT   SAVE 

Slightly wonky idle, RPM surging during acceleration 900

posted by  MisterBLC on  Tue Jan 14 15:41 CST 2014
Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
last visit: Tue Aug 26 14:55 CST 2014
[RELATED]

Everyone,

I have been diagnosing an on-going issue with my wife's '94 940 Turbo. I have been slowly doing a level 0 on the car, but this issue has been persistent. The main problem is that during hard acceleration (especially when cold or under load when going up a hill for example), the RPMs will surge and you will get pulses in the acceleration of the car. You can see this on the Tach, the RPMs will surge by as much as 250 when the problem is particularly bad. Only other issue with the car is a wandering idle that stubborningly sticks around, despite cleaning of the throttle body and IAC. What has been done so far:

- Recent stage zero (~1 year ago): new plugs/wires, new dizzy cover, new timing and accessory belts, IAC and throttle body cleaned, PCV system cleaned, vaccuum lines replaced with silicone.
- New turbo (replaced due to large throttle shaft play and whining noise)
- new ignition coil
- Relatively recent (~3 years) replacement of RPM speed sensor on the back of the block

I'm some what at a loss...I am thinking of trying a new IAC to help clean up the idle, but I am not sure if this could be causing my acceleration surging. Only other idea I had was that I was getting intermittent knocking during hard acceleration and the timing was being retarded, causing the surging. Is there an easy way to see if the knock sensor is detecting knocks? Any other ideas on possible sources of the problem?

Thanks,
Brian








  •   REPLY TO THIS MESSAGE Replies to this message will be emailed.    PRINT   SAVE 

    Slightly wonky idle, RPM surging during acceleration 900

    posted by  MisterBLC on  Tue Jan 21 11:18 CST 2014
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Tue Aug 26 14:55 CST 2014
    [RELATED]

    Sorry for the slow reply, I was out of town last weekend :) 215K Miles on the car, forgot to mention that!

    - rstarkie: Unfortunately you cannot just unhook the knock sensor as this would cause the computer to throw a code and retard the timing all the time.

    - Will, those are some good ideas. Fuel pump is original or at least not replaced in quite a while (don't have full maintenance records). I have recently replace the fuel filter however. I was thinking it may be transmission related but didn't have a good test...I will try that this week. EGR is another great idea...the EGR valve has not been cleaned recently, and I am kicking myself because I recently had the intake manifold off. I am wondering...can I disconnect the vacuum line to the EGR valve to prevent it from inject gas? Alternatively, any easy way to block off the EGR system temporarily to see if this is the problem? After 215k miles, I can definitely see the EGR valve developing an intermittent problem!








  •   REPLY TO THIS MESSAGE    PRINT   SAVE 

    Slightly wonky idle, RPM surging during acceleration 900

    posted by  rstarkie on  Wed Jan 15 07:18 CST 2014
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Fri Oct 24 10:14 CST 2014
    [RELATED]

    I am not familiar with how the knock sensor functions but I wonder if you could simply disconnect the sensor and take a test drive to see if the problem persists?

    Randy








  •   REPLY TO THIS MESSAGE    PRINT   SAVE 

    Slightly wonky idle, RPM surging during acceleration 900

    posted by  Will740turbo on  Wed Jan 15 00:51 CST 2014
    Author: [PROFILE] [EVERY POST] [THREADS] [BEST POSTS] RSS Feed     [IGNORE ALL POSTS]
    last visit: Wed Oct 22 16:09 CST 2014
    [RELATED]

    How many miles on the car?
    Do you have an idea of if the fuel pump is original?
    Could the transmission be slipping? (Press the brakes and gas together, and see if the RPMs climb significantly without the speed increasing. Don't brake so much that the car slows down, you just want to place a bit of load on the engine.)

    Does the turbo boost needle surge before the rpms do?

    It being a turbo, does it have an EGR? Have you ever checked/cleaned the EGR or its vacuum control solenoid? If the EGR valve suddenly adds less exhaust to the mix, the engine speed will increase.

    It's an interesting problem.







<< < > >>



©Jarrod Stenberg 1997-2022. All material except where indicated.


All participants agree to these terms.

Brickboard.com is not affiliated with nor sponsored by AB Volvo, Volvo Car Corporation, Volvo Cars of North America, Inc. or Ford Motor Company. Brickboard.com is a Volvo owner/enthusiast site, similar to a club, and does not intend to pose as an official Volvo site. The official Volvo site can be found here.