ECU 153 has a worse idle than 173?

[IS300E30]

I keep reading that the ECU 173 has a better idle than 153, but I cannot find anywhere on how it is better?

Can anyone that made the switch provide me some information on how the 153 was, and once you switched to the 173 on how it was improved?

[reelizmpro]

153 is Motronic 1.1 (dual board) on the early 87-88 325i cars originally. Then 89-on 325i's came with a bunch of Motronic 1.3 (single board) DME's such as 173, 525, 380, etc. These had more diagnostic capabilities and are said to have better idle characteristics. I had a stock 88 325iS years ago with a 153 but never saw a need to switch over to the later DME's. When I drove later 325i's I noticed the idle speed was lower and perhaps more stable.

[Panici]

I did the 153 -> 173 swap on my M20 years ago. It was plug-and-play on my 1987.

Idle is smoother and more consistent with the upgraded ECU.
Responds better to throttle input and recovers better with load changes (electric fan, A/C, etc).

[IS300E30]

I did the 153 -> 173 swap on my M20 years ago. It was plug-and-play on my 1987.

Idle is smoother and more consistent with the upgraded ECU.
Responds better to throttle input and recovers better with load changes (electric fan, A/C, etc).

I would LOVE a smoother idle. Mine does not fluctuate, but it is still rough.

Any negatives that you saw going to the 173?

Did you just buy a straight used one or did you buy a refurbished?

[Panici]

I would LOVE a smoother idle. Mine does not fluctuate, but it is still rough.

Any negatives that you saw going to the 173?

Did you just buy a straight used one or did you buy a refurbished?

Bought a used one from ebay for $40, and it came chipped with a Dinan 91 octane tune.
This was 10 years ago now so prices are likely different.

From my build thread:

Updates:

• 153 to 173 ECU conversion
  • Upgrade to Motronic 1.3
  • Came with a Dinan 91 octane chip!
    • Raised rev limit, and pulls noticeably harder on WOT.
  • Idle is improved.
  • I also noticed torque converter lockup for the autotragic is slightly different
  • I now also have the "stomp check" for ECU codes.

[e30davie]

I would LOVE a smoother idle. Mine does not fluctuate, but it is still rough.

Any negatives that you saw going to the 173?

Did you just buy a straight used one or did you buy a refurbished?

I doubt BMW sold your car with a rough idle. I don't think its the ecu...