Engine Surge w/ Air blowing cold when set to full temp.

[Delta-Tango]

Got a petrol 2006 1.8L MR2 Mk3, with no mods. roughly 63k miles

When idle after driving for a few mins, the engine pulses, or surges.

Rev counter is normally at 900 - 1000, but drops to around 700 and back up again (all at the beat of either 120bpm yesterday or 200bpm this morning if that's relevant).

This happens regardless of the air blowing cold (when set to full heat temp.) if I leave it off after a while, it's hot for less than a minute.

Had a full+ service from toyota dealership (they clean the engine and replace all liquids - apart from petrol haha) and passed MOT all clear back in December 2017.

Noticed the engine coolant level is wayyyyy above the full line but not had any problems until yesterday.

Please advise. I'm not a mechanic by all means, so layman/noob/idiot terms without the insults would be appreciated.

[jkh112]

I am not sure I understand what you mean by the air blowing cold, but it makes me wonder if it is the aircon kicking in making the revs drop.
Does the idle speed surge if you have the aircon/climate control turned off?

[Delta-Tango]

When I set the car heater fans going, the air blows cold even when I set the temperature on full heat.

The engine surges even when the air isn't blowing at all.

[Johnnybee]

Possible airlock in the cooling system causing a coolant temperature sensor to give incorrect readings causing the idle to rise and fall? An airlock would also cause the heaters to blow cool.

[Delta-Tango]

i guess the tubes on the radiator ends is the way forward?

[Gad-Westy]

Johnnybee said:

Possible airlock in the cooling system causing a coolant temperature sensor to give incorrect readings causing the idle to rise and fall? An airlock would also cause the heaters to blow cool.

Yep. Would also explain the high coolant tank level. Giving all of the coolant hoses a very good squeeze can sometimes be enough to dislodge and airlock but they can also be right pain, especially air in the heater matrix.

[Delta-Tango]

Took cap off, squeezed tubes and noticed loads of air bubbles come out. Keep squeezing, get syphon tubes or am i missing something else as well?
Best with engine off?

[Delta-Tango]

took it for a drive, engine is idling fine now but
blowers only heat up if im moving and doing 1200+ rpm. they go cold when car is still.

faulty sensor?

[Mr2Mike]

Delta-Tango said:

took it for a drive, engine is idling fine now but
blowers only heat up if im moving and doing 1200+ rpm. they go cold when car is still.

faulty sensor?

More likely you still have an airlock, or the heater core is partially clogged.

[anonymous-user]

Delta-Tango said:

took it for a drive, engine is idling fine now but
blowers only heat up if im moving and doing 1200+ rpm. they go cold when car is still.

faulty sensor?

Heater matrix clogged with crap and/or faulty thermostat I would say.

(No experience of MR2 but worked on a few cars )

[E-bmw]

As above or water pump impeller goosed, walk away, it has more than likely overheated to one extent or another.

[Gad-Westy]

BAM225 said:

Delta-Tango said:

took it for a drive, engine is idling fine now but
blowers only heat up if im moving and doing 1200+ rpm. they go cold when car is still.

faulty sensor?

Heater matrix clogged with crap and/or faulty thermostat I would say.

(No experience of MR2 but worked on a few cars )

Yep, clogged heater matrix sounding very plausible. Drain coolant, detach hoses as close to heater matrix as possible and use mains pressure hose to flush it through in both directions and then fill cooling system back up by whatever the internet wisdom dictates for that particular car. Last bit is important as many cars very easily get air trapped if you don't fill it correctly. Six cylinder BMW's are a right pain for this. It's often a good idea to fill cooling system with header tank as high up as possible, possibly by parking on a hill or ramps.

[anonymous-user]

Gad-Westy said:

BAM225 said:

Delta-Tango said:

took it for a drive, engine is idling fine now but
blowers only heat up if im moving and doing 1200+ rpm. they go cold when car is still.

faulty sensor?

Heater matrix clogged with crap and/or faulty thermostat I would say.

(No experience of MR2 but worked on a few cars )

Yep, clogged heater matrix sounding very plausible. Drain coolant, detach hoses as close to heater matrix as possible and use mains pressure hose to flush it through in both directions and then fill cooling system back up by whatever the internet wisdom dictates for that particular car. Last bit is important as many cars very easily get air trapped if you don't fill it correctly. Six cylinder BMW's are a right pain for this. It's often a good idea to fill cooling system with header tank as high up as possible, possibly by parking on a hill or ramps.

Funnily enough my reference for thermostat or heater matrix was 6 cylinder bmw's. Gotta love the brittle cooling system

[Delta-Tango]

Got a 2nd (professional) opinion. He's saying it's not affecting engine overheating or anything mechanical cos the fans are working, even though the engine does surge a little still, but not as bad as before I squeezed the tubes to get bubbles out.

His final verdict: Either heater matrix or water pump but only way to tell is to strip it all down which he couldn't quote cos "it's a big job and needs a specialist, which I'm not."

[Gad-Westy]

Delta-Tango said:

Got a 2nd (professional) opinion. He's saying it's not affecting engine overheating or anything mechanical cos the fans are working, even though the engine does surge a little still, but not as bad as before I squeezed the tubes to get bubbles out.

His final verdict: Either heater matrix or water pump but only way to tell is to strip it all down which he couldn't quote cos "it's a big job and needs a specialist, which I'm not."

Surprised he's saying that. You can normally get a good idea of whether a water pump is doing it's job by squeezing the top rad hose while engine is warm with a few revs on. You can normally feel the movement of coolant inside.

It's also not a big deal to flush the cooling system though I appreciate access is probably trickier on an MR2.

But anyway, I doubt it's the water pump failing for a few reasons. Firstly, because with the water pump not working, your coolant would generally be quite warm throughout the system so you'd get heat from your heater and because you said that you get more heat from heater with some revs on than you do at idle. You'd also expect the car to be overheating.

I'm also not 100% convinced your two problems are related but they could be. I'd fix the cooling issue first as it sounds like an air lock which really ought to be sorted sooner rather than later. Suggest you find another garage and ask them to replace the coolant and flush the system at the same time. It really shouldn't cost you much.

[Gad-Westy]

BAM225 said:

Gad-Westy said:

BAM225 said:

Delta-Tango said:

took it for a drive, engine is idling fine now but
blowers only heat up if im moving and doing 1200+ rpm. they go cold when car is still.

faulty sensor?

Heater matrix clogged with crap and/or faulty thermostat I would say.

(No experience of MR2 but worked on a few cars )

Yep, clogged heater matrix sounding very plausible. Drain coolant, detach hoses as close to heater matrix as possible and use mains pressure hose to flush it through in both directions and then fill cooling system back up by whatever the internet wisdom dictates for that particular car. Last bit is important as many cars very easily get air trapped if you don't fill it correctly. Six cylinder BMW's are a right pain for this. It's often a good idea to fill cooling system with header tank as high up as possible, possibly by parking on a hill or ramps.

Funnily enough my reference for thermostat or heater matrix was 6 cylinder bmw's. Gotta love the brittle cooling system

Yep, my 330 had a blocked heater matrix all through winter. Tried all sorts of bleeding techniques. Some worked five minutes, some not at all. Only fixed it when I eventually did the hose pipe trick.

Had similar issues on my 528 as well

[E-bmw]

Delta-Tango said:

blowers only heat up if im moving and doing 1200+ rpm. they go cold when car is still.
faulty sensor?

Had exactly this several years ago (forget the car) the water pump impeller had basically rusted to next to nothing & was only moving about 1/2 as much water as it should.

In winter the car was cool enough to keep the engine temp down but not moving enough water to fill the heater matrix until at speed.

[Delta-Tango]

All sorted - my radiator had been completely worn away. Replaced it and the coolant, works fine now