1999 S70 GLT, hard time starting, intermittent RPM, misfires

[z80]

Hello! Thank you for the support! I appreciate it a lot!

Did you ever change the fuel pump relay? My buddy was getting random stalls and loss of power and it threw an ETM light. He has replaced the ETM twice now with junkyard units, but it returned again. This time he swapped the relay and the car has been running well since then.

I did. Right before replacing the ETS sensor. The car was behaving like you've described: loss of power, shaking. And there was no ETS light by then. It was cheap so I gave it a try. As soon as it started turning ETS light on, I replaced the sensor.

Even though I don't quite understand how it could it be (the pressure doesn't drop), I see what you are saying about a pump relay. I'll try swap it with the old one and see what happens.

Thank you for sharing the experience!

I'm still wondering how that works. Does it basically bypass the signal?

That's my understanding. The instruction says to physically disconnect the 2-d sensor output from the throttle module's input and instead route the output of the replaced sensor to the throttle body input terminal. The 2-d sensor output remains disconnected and 1-st sensor feeds both inputs with one and the same signal.

[scot850]

Thanks for that info, as it is the first time I have seen that and it means actually doing this mod is not too terrible. Also the video how to's while most a terrible, they generally give enough info for me to want to try this at some point. I know my buddy has at least 2 for NA motors that could be rebuilt. I'll just have to add that to my seemingly endless list of 'projects' awaiting attention.

Neil.

[z80]

Hello!

I tried using a different fuel pump relay as recommended. But, unfortunately, that didn't seem to help much.

Also I've triple checked the throttle module, pulled the socket back-forth a few times, and tried turning the plate by hand while observing the throttle position sensor: default position = 19.61%, fully closed = 0%, fully open = 100%. ETS light didn't come back so far. I guess, it might have been a fluke due to excessive engine shaking...may be...

NEW DATA

Today the car has been transitioning to this ready to die state and back a few times. And I was able to record data while it was doing so. Basically, when the car suddenly decides that life is too challenging, the MAF signal instantly jumps from 4g/sec to 12 g/sec, see below marked with red line. Before the moment MAF signal jumped up, the car RPM was stable around 850. And right after it started struggling and jumping between 600 and 400.

Per my understanding, in order to keep stoichiometric ratio for lower RPM, air flow has to be lower, not higher. Right? Also, if it was a bad connection in MAF socket, the signal could only drop, but not go higher. My current belief is that something has either stuck to the sensor and causes incorrect readings or the sensor is on the way out.

Based on the data does the MAF theory sound legit?

[scot850]

Go hunting for a new MAF or junkyard one. These are no longer available from Bosch, so junkyards or ridiculous priced Volvo one are your options.

Neil.

[abscate]

You don’t get good data during cranking , there are too many things fluctuating both mechanical and electrical. You can try a junkyard MAF ( Bosch for your turbo) but I doubt that is it.

I don’t fool with sensors on the ETM since the Volvo contactless one came out in 2012..see the ETM Room forum for part number. About $150 on ebay

[z80]

You don’t get good data during cranking , there are too many things fluctuating both mechanical and electrical. You can try a junkyard MAF ( Bosch for your turbo) but I doubt that is it.

Hello! Thank you for the advice! The data on the picture has been captured when the car was idling. The jump in MAF signal is what it does on its own with me being outside unable to touch any controls. And when it happens, the RPM goes down, not up, it almost stalls.

I don’t fool with sensors on the ETM since the Volvo contactless one came out in 2012..see the ETM Room forum for part number. About $150 on ebay

Yes, that's what I've done per your recommendation around November 2022. BTW, thank you so much again! Throttle sensor has been working since then. And I've at least partially validated that it still works by turning the throttle plate by hand and observing the "Throttle position %" OBD signal with engine off and key in position II. Of course, it may have an intermittent problem happening only when the car runs... But I'm not really sure how to validate throttle position on a running car.

[scot850]

I know Abscate doesn't like doing this, but have you tried disconnecting the MAF while the car is idling to see what happens? The ECU tries to adapt to preset settings when there is no signal from the MAF. It may at least eliminate the MAF as being an issue or not. A cleaning of the cable connector on the MAF and MAF cleaning may also help. Only use MAF cleaner and don't drown it!

Neil.

[z80]

Hello! I don't feel comfortable pulling electrical connectors on a running car. But I tried starting the car with and without MAF connector plugged in.

NEW DATA

1) Started the car a few times with and without MAF connector plugged in. It seems it is irrelevant. It still randomly switches to struggling and back to normal.

2) I've noticed that the car started turning the radiator fan on each start and turning it off ~10 seconds after. The temperature sensor is recently replaced with an OEM one.

3) After a few start/shut down cycles the car's refused to shut the radiator fan down at all with motor off. I've pulled the middle fan relay connector to make it stop.

4) With fan off I was able to hear that, instead of whining, throttle was interchangeably clicking, whining, and making this last loud click repeatedly and seem to be unable to shut down at all.

5) Another whining the car makes usually from the firewall area also didn't ever stop. (I feel shame, but I still don't know what it is exactly. I guess its a fan???)

6) I've disconnected the negative battery terminal and held the car de-energized for a couple of minutes.

7) I've reconnected the battery terminal and started the car. The first time it had some hesitation starting but didn't try to stall.

8 ) I drove it for about 40 minutes. So far it didn't try to stall at all.

9) While driving, I've been monitoring "throttle position %", "MAF g/sec", "STFT", and "LTFT". I haven't noticed any outstanding anomalies. May be one thing which attracted my eye is at constant speed sometimes MAF is almost constant but sometimes oscillates with relatively small amplitude +/- 0.5 g/sec with average being at about 18 g/sec at 55 mph. Might it be a process of adaptation?

10) Strange thing is before de-energizing the car "LTFT" was stable at around "+6.3"%. Now after de-energizing and driving for 40 minutes it is at "-0.5%" with "STFT" wiggling around 0%.

I'll check it again tomorrow when it cools down. Might it be it is just going cuckoo because of old age?

[rrres]

Have you tried a compression test and a leak down test?

[z80]

Have you tried a compression test and a leak down test?

Hello! Thank you for a hint! No, unfortunately, I haven't tried those. I could have rented the compression test kit and test it. But, as for the leak down test, I don't have a compressor to feed the test tool.

New information

I've been testing the car for two days in the morning and at night both idling and driving. So far after disconnecting the battery terminal the problems seem to not come back as of right now. So far this is the strangest things I've ever observed. I'll keep testing it and if the problems indeed have gone away I'll declare it a fix.