Volvo b234f high idle

[cableman]

So recently the car had a service ar a trusted volvo shop, and the repair was on the sunroof and the PCV system. I suppose the hoses were routed wrong.. Now after that when the car warms up and I'm cruising on the highway when I come off the highway and decelerate, the rpms drop to like 1000 from like 2200 in like a pulse, almost 100 percent consistent. Now, I don't have any fuel or spark issues that I know of because the car ran ok ish before I could feel some sluggishness but the pcv fix I guess helped it? After I finish pulling off the highway or any cruising rpm, the idle is now like 1100+ even sometimes 1500, it's somewhat consistent within its runtime but when you turn the motor off when it has a high idle, and turn it back on it goes back to like it's normal 650.. Is this a bad IAC? The previous owner said he has been messing with high idle issues but got a sorted and now its back to haunt me....

Any help?

 

[940 16 valve]

I remember chasing an issue like that with my B234 and it ended up being a bad ECU.

But first I would:
-check the throttle position switch with an ohmmeter with it warmed up like when it acts up
-pull and check the idler motor to see it it's moving freely
-Check for intake leaks - especially the hoses for the idler motor, try flexing them to see if there a crack hiding
-Check throttle stop adjustment

Good luck!

 

[jonaix]

I am nearing the ability to sell a xx928 ECU if you need one, waiting on my xxx51 ECU with chip from redblockpowered
I had had this issue you describe and remember there being a armature issue, or cable pulley issue with throttle. Sorry, also the engine wiring harness was somewhat to blame, now I remember, a cable heated through and melted and was maintaining voltage to the IAC. I would recommend DaveBarton's Engine harness.

 

[bobxyz]

LH2.4 can have a high idle if the speedometer VSS signal to the ECU isn't working. This will show up if you go over ~3K rpm with some load (or just drive around a bit with the overdrive off), and will immediately go back to a normal idle if you shut the engine off, count to 10, and restart it.

edit: if you check the ECU diag codes (socket #2) when it has high idle and before shutting it off, it will have a 3-1-1 VSS Missing code if this is the issue. A 3-1-1 won't turn on the check engine light.

 

[oldschoolvolvo]

^^this

 

[cableman]

LH2.4 can have a high idle if the speedometer VSS signal to the ECU isn't working. This will show up if you go over ~3K rpm with some load (or just drive around a bit with the overdrive off), and will immediately go back to a normal idle if you shut the engine off, count to 10, and restart it.

edit: if you check the ECU diag codes (socket #2) when it has high idle and before shutting it off, it will have a 3-1-1 VSS Missing code if this is the issue. A 3-1-1 won't turn on the check engine light.

What is the 3 1 1 code for? Like what needs to be replaced passed that?

 

[bobxyz]

3-1-1 is VSS Missing code. For the US 240's, it could be due to a poor speedo wiring connection.

What year/model? Does your speedo work?

 

[cableman]

3-1-1 is VSS Missing code. For the US 240's, it could be due to a poor speedo wiring connection.

What year/model? Does your speedo work?

It's a 98 740 gle and yeah the speedo does work it's just the mileage doesn't

 

[cableman]

3-1-1 is VSS Missing code. For the US 240's, it could be due to a poor speedo wiring connection.

What year/model? Does your speedo work?

Also when the high idle happens the ecu shows 1 1 1 as a code that means no codes correct?

 

[bobxyz]

Yup, 1-1-1 on ECU socket #2 before turning it off means no codes, so it's not the missing VSS problem. You could check for EZK codes (socket #6) but that's probably OK too. Sorry, on to the next idea....

 

[ZVOLV]

Check socket 6.

Speedo working but odometer inop could mean the signal OUT of speedo to ECM is no good. You'd have to check at the ECM. Scope, meter.

Both my 740s have high idle, and both have speedo issues

 

[cableman]

Check socket 6.

Speedo working but odometer inop could mean the signal OUT of speedo to ECM is no good. You'd have to check at the ECM. Scope, meter.

Both my 740s have high idle, and both have speedo issues

I will say it also has a hot start issue like it won't start sometimes when it's at operating temp, no codes or anything

 

[oldschoolvolvo]

Check the ignition powerstage. Thermal paste between module and heat sink may have deteriorated and need reapplied. I had a similar hot start issue and this solved it.

 

[cableman]

Check the ignition powerstage. Thermal paste between module and heat sink may have deteriorated and need reapplied. I had a similar hot start issue and this solved it.

Yeah I can see that once it cools down she starts up perfect, is that bolted to the firewall correct?

 

[oldschoolvolvo]

I'm not as familiar with the 7/9xx series, but I believe the power stage is on the fender near the battery.
(photo from 240turbo.com)

 

[cableman]

I'm not as familiar with the 7/9xx series, but I believe the power stage is on the fender near the battery.
(photo from 240turbo.com)

It's on the opposite side deep under the intake cleaner box well out of sight, I put some thermal paste under it to the frame and a bit around where it mounts to the heatsink, wasn't able to take off the cleaner box as it started pouring raining. The engine has no codes so hopefully it just this module causing it to surge when letting off the gas and no start hot starts 🤷‍♂️

 

[oldschoolvolvo]

When you have a chance you really should take the unit out of the car, separate it from the heat sink, clean both halves and put new thermal paste between the power stage and the heat sink (not between power stage and fender).

Just for reference, this is what I used when I refreshed mine.
Arctic Silver 5 AS5-3.5G Thermal Paste https://a.co/d/2D5VFsM

 

[cableman]

When you have a chance you really should take the unit out of the car, separate it from the heat sink, clean both halves and put new thermal paste between the power stage and the heat sink (not between power stage and fender).

Just for reference, this is what I used when I refreshed mine.
Arctic Silver 5 AS5-3.5G Thermal Paste https://a.co/d/2D5VFsM

Perhaps since it's been doing this for a long time and I am just now getting to it should I just up and replace it or just try cleaning it first?

 

[cableman]

When you have a chance you really should take the unit out of the car, separate it from the heat sink, clean both halves and put new thermal paste between the power stage and the heat sink (not between power stage and fender).

Just for reference, this is what I used when I refreshed mine.
Arctic Silver 5 AS5-3.5G Thermal Paste https://a.co/d/2D5VFsM

Also update* what I did didn't help, however bot sure if they are related to hot start but my car started right up after a decently long drive? 🤞

 

[oldschoolvolvo]

Perhaps since it's been doing this for a long time and I am just now getting to it should I just up and replace it or just try cleaning it first?

My vote is to try and clean it and re-apply the thermal paste if you already have it.