On my 98 v70 I had the intermittent stumbling with some rpm drop, no codes, but bad gas mileage. I replaced the thermostat and coolant temp sensor, but used a CTS that is not original volvo dealership, now I have the CTS code and the stumbling problem again, it ran great for the first 50 miles. Does it really matter which brand I use for this, its only a brass temp sensor. Im leaning toward that being the problem since the car usually hates other aftermarket parts( spark plugs, rotors, pads etc..).

There are specs for the resistance across the terminals of the CTS. It's been years since I did it, but I believe I found them on the internut, so you may also be able to find them.

As I recall the resistance at ambient temp is supposed to be on the order of a few thousand Ohms, but the faulty part I replaced was basically open (little to no resistance). I do not recall the make of the replacement. I buy from FCP and don't specifically seek out OEM parts.

What led you to replace the CTS? If you lacked other symptoms like a wacky water temp guage or radiator fan that runs too much then I would chase the other probable causes that Klaus mentioned.

-Will
--
850 / Mini

An open in an electrical circuit is infinite resistance, as in no continuity, closed or shorted is little to no resistance.

Mark

no messgae inside

Did a search, came up with this:
http://www.brickboard.com/AWD/volvo/754697/850/true_overtemp_instrumentation_error.html

From that post:
"Before replacing the engine coolant temperature sensor,
test the electrical resistance with an ohmmeter: here's the specs

0?C (32?F) 7300 Ohms
20?C (68?F) 2800 Ohms
40?C (104?F) 1200 Ohms
80?C (176?F) 300 Ohms
100?C (212?F) 150 Ohms
"

Yay BB search engine.

Good luck,
-Will
--
850 / Mini

OEM parts are usually better than aftermarket in some cases. It all depends on quality control. If you put in a generic ECT sensor, it may be bad. Does your temp gauge in the instrument panel work correctly?
If you saved your original ECT sensor, put it back in before you buy another. Then start looking for vacuum leaks, especially at the elbows and other vacuum line connectors.

Klaus
--
The 164 has a new home, all I am left with are a 95 854T and a 98 V70R :)

I forget who it is that makes the ECT sensors for Volvo but they have problems making a good one themselves and the aftermarket ones are even worse. Factory Volvo ECTs, A/C pressure switches, and ignition contact plates are probably the three components that I have to parts warranty more than anything else. I guarantee my work for 1 year unlimited miles and I know for sure that I did at least 3 of those factory temp senders under warranty last year alone. Don't ask me how in the hell a solid brass component manages to leak coolant right through the middle of it but they do, the later style S40 sensors are little better too. Put a factory one it and go from there.

mark

I used an aftermarket sensor on son's 98 S70GLT and it died within a few thousand miles. Put in a Volvo and it has been ok since.

dick

So I had a replacement fuel pump that I put in just for maintenance( I know Im wierd), cleared the codes, and now havent had any drivability issues and no code appearing. 70 miles of driving and it has been running great, lets see how long it lasts.

The reason I changed the CTS is because of a search I did and the very intermittent stalling problem I had where the rpms would drop to 600 and jump back up like it was getting too much fuel at one time. Because of that problem I have replaced the MAF, power stage, plugs/wires/distributor, and CTS, Ive also cleaned the idle air motor and have done a relativly good search for vaccum leaks. Every part seemed to help the intermittent problem become more intermittent, but not fully cure it. Hell it probably is vaccum, I will have to go looking further, I figure with these miles and age of car I cant go wrong replacing parts.