Hi all,

I am trying to diagnose a rough idle on cold start with my 1990 DL (nonturbo) with code 121.

Little history:

I picked up this car a few months ago in a decent condition, but it needs some love. The mileage is unknown, but I am sure it is well above 200K, maybe close to 300K. It drove ok for a week, and I was excited to start fixing a few issues with it to use it as a daily driver until the CI light came on! I have always owned Japanese cars with OBD2 and never had an issue (shocking), but I don't want that to discourage me from working on my new to me Belouga!

The issue:

I tried to start it after work; it starts and immediately dies. Luckily, it was parked in my office garage, so I was able to limp it home by disconnecting the MAF.

My attempts:

1- I replaced the MAF sensor with Bosch from eBay, it did not work, the new Bosh was too expensive, so I opted for a Delphi MAF

Amazon

Amazon

2 - I cleaned the TB and replaced the gasket while I was there, but ended up with an issue (The car has no power when I accelerate but will pick-up if I baby the throttle) so I replaced the TPS with one from Rockauto, and the issue is gone.
3- Cleaned the idle control motor with carb cleaner.
4- Replaced the spark plugs with Bosch 7900.
5- Plugged the two vacuum hoses on the driver side, going into the TB. Also, the tube that goes to the cabin (I heard a hissing noise when I step on the gas peddle)

I disconnected the battery after each step to clear the codes and got different code/codes each time. Here are the ones I know.

• 321
• 231
• 221
• 113

The most recent one is 121, which is still on. The car runs fine after it warms up, but I still think it lacks power on initial acceleration; I don't have a fully functional 240 to compare it to, hahaha. I don't know what could be causing this issue and would like to know if someone else had the same problem.

Thank you!

 

the 121 is reporting on the lack of a MAF signal. check the connector/wiring and if you can't clear it, see what happens if you put the original MAF back in. As to a general cause, test the ECT sensor to make sure its resistance is ok when cold (google for charts) and you may need a smoke test for an intake air leak if you think the MAF is good.

 

When I plug the old MAF the car will not start. If I start it and plug it in, the car dies immediately. With the aftermarket, I see a difference (rough idle) when I unplug it.

 

hot plugging the MAF when the ignition is on can damage either the MAF or the ECU

 

I have not heard any good things about the aftermarket MAF sensors. Bosch is the way to go but buying off eBay is a crapshoot. I used to pick them up at the junkyard when I would see one. They would sell them to me for $25-35 which was cheap enough for me to take a chance on them. I would pick them up when I would see them and keep them for backups. However, it's been over 5 years since I have seen a 240/740/940 in the junkyard near me.

Regarding the hissing noise when stepping on the accelerator, that is due to a faulty vacuum check valve. It's the black/white cylindrical piece that connects to the hose that runs into the cabin to run the hvac valves. Fairly cheap to replace.

 

I did not know that. Thanks for the tip.