130k 1.9t 2003 s40. Here's some back story to help with diagnosis. Bought this nightmare if a car two years ago as a salvage title for my wife. Having never owed a Volvo before I noticed that the radiator fan kept turning on so I thought maybe it was running hot so I replaced the thermo stat and temp sensor along with the anti freeze. I work for napa so I used napa parts. Well having talked to another s40 owner I found out that the fan coming on all the time is normal. I also replaced the timing belt plugs and coil packs around the same time as the thermostat and temp sensor. Around two years ago. Also I think its important to note I bought the car with the check engine light on with about 6 codes. Here are the codes. I haven't got to any if the codes in the last year having run out of money and the car being drivable so I'm guessing these are still present. This next part I copy pasted from a previous post cause I couldn't remember all the codes. But my actual problem will be below the codes. Thanks for your patience. I'm also doing this at work so I these any spelling errors I apologize.


1 p0101 MAF, faulty signal (should I just replace or check for signs)

Troubleshoot: I cleaned MAF with clear changed air filter

Stored codes:

1: P0101: same as above this is how my code reader reads them main code, stored,and pending...

2: p0107 Boost sensor signal too low

3: p128 coolant temp sensor faulty sign
Troubleshooted; when timing belt was replaced had new thermostat put in but didn't replace temp sensor although I do have the sensor I just haven't installed but will.

4: p0600; serial communication link
What I was told about this one was pervious owner didn't flash ECM correctly. Now car is a salvage title with airbag deployment. Air bags are reinstalled but they never got the airbag light turned off from the dealer so maybe since the airbag think they are deployed this could be ECM code issue?

Throubleshotted nothing to this point

5: p0602; power train control module programming error
Probably has to to with previous code 0600 so my guess about airbag light being on for 0600 is prolly wrong

6: P0700 DTC stored in the transmission control module
Troubleshooted; nothing

7: p0723 transmission speed signal missing
Throubleshooted; checked speedometer, works fine.

Pending Codes

1: P0101

2: p0107

3: p0128

4: p0700

KEEPP in mind I THOUGHT IT WAS IMPORTANT INFORMATION LEADING TO MY PROBLEM I HAVE TODAY and I apologize for the log post those are codes I posted from a previous post.. Ok here's the issue I'm trouble shooting. The temperature gauge randomly drops and it accelerates by itself for about two or three seconds causing the car to lurch foreword. I noticed that it only happens when the temperature gauge drops in temperature. It's almost dangerous to drive. I also notice that the temperature doesnt reflect actual engine temps because it says it's still cool from cold start and take awhile before actually reading correct temperature. Problem is intermittent, some time doesn't happen at all but if I'm not paying attention and the car lurches foreword at the wrong time you can see were my worry comes from . Has anyone had any issues like this? Thanks you for reading this and for any help you can provide.

 

The bleeder screw on the lower radiator hose was busted by previous owner. So someone suggested that maybe an air pocket is hitting the temp sensor and causing the drop in temp randomly causing the temp to drop and thus the engine thinks its cold causing the fuel air mix to change causing the sudden acceleration. The hose is special order and 5 days away. I'd like an opinion on the also before I order that part.

 

Come on man, change the temp sensor, reset the codes and see what returns. SMH

You will likely need to replace the MAF if you still get that code.

Both of the issues you have control fuel/air mix and will cause drive ability issues.

 

You on your period? Well I was hoping to hear from someone that this had happen to before I go replacing 1 year old temp sensor. That's where I was going to start anyway was the temp sensor being its only 5 bucks. I don't have a code reader and like I said those codes are from a year ago. Just wanted to give more info rather than less info. But if anyone else has had this happen if love to hear from you instead of throwing parts at it... No need to be rude either, people who are rude on forums obviously spend to much time on them...

 

I have read the constant running fan is a bad MAF. I have not experienced this myself as of yet.