How often do I need to clean EGR?

Every 50k miles is reasonable.

What do you mean by "EGR issues". Also, "kitchen cleaner"? FWIW, your EGR issues "may" be the onset of head gasket issues. 120K is a bit early, but...

For everthing but the EGR cooler, brake cleaner (aka parts cleaner) is sufficient, and preferable. Using the cleaner in conjunction with brushes and rags.

For the EGR cooler I'd suggest a caustic cleaner. Being stainless steel, and having such a convoluted interior, caustics are the go-to. Oxi-Clean Versatile Stain Remover is effective, and safe for skin. Not sure if it'd be available in UK though. Something that will be very effective, but needs caution, is a lye solution. To minimize the amount needed, use an inert rubber stopper in one end, prop it up and pour in the solution. It'll take a cup at most. Alow to sit about an hour, rinse out and repeat. For reference if buying a stopper, the smaller end opening is approx 21 mm diameter.

Purchasing lye is getting a little tricky in North America; I believe it's an ingredient in methamphetamine production? I might have missed that Breaking Bad episode. Anyway, still available on Amazon, for soap making use here. Hopefully also so in UK.

Have you been cleaning the intake manifold too? It's the final leg of the EGR path, has a main gallery where the flow enters, and capilaries for each port. Again, only use some sort of brake/parts cleaner, nothing caustic. The intake has embedded pieces that WILL react with caustics.

Top two links in my sigature are EGR related. If you're on a phone turn it landscape to see signatures.

Here's a cleaning workflow I drafted a whiles back, intake manifold is relatively straightforward, not mentioned in the following:


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EGR cleaning workflow:

1. Remove wipers, lower windshield trim, wiper motor/linkage, and underlying metal cowl. See NutzAboutBolts excellent video for details:

2. Drain 2 quarts(or liters) from radiator drain spigot, into clean container (to be reused). This will drop the coolant level below the EGR system, allow disconnection of the EGR COOLER coolant hoses without spillage.

3. Remove bottom nut from EGR COOLER bracket. This can be done first (or even days earlier) , and due to the difficulty in accessing/removing it, I'd recommend to leave it off; the cooler is quite secure without it.) If you want, back out the stud at that location too, and leave it off permanently as well. (If the doing the latter, it will not be necessary to remove the 2 studs at egr cooler to exhaust manifold connection, and the studs will help retain the gasket.)

4. Remove engine air intake snorkel, and air filter box.

5. Remove EGR PIPE. There are 2 bolts at each end, and an additional bolt holding a plastic cover piece at the intake manifold end that needs to be removed first.

6. Disconnect electrical connector from EGR VALVE.

7. Disconnect coolant hoses from EGR COOLER.

8. Remove front/top nut from EGR VALVE, and associated stud.

9. Remove (2) nuts from rear flange connection of EGR COOLER, and associated studs. Be careful to catch the gasket between EGR COOLER and exhaust manifold: it will be loose once the studs are removed. Note: if the stud removal described in step 3 has been done, removal of the rear studs is not necessary.

10. Remove top/centre retaining bolt from EGR COOLER. The EGR VALVE/COOLER assembly should now be loose, able to be lifted out. Be careful not to tip it too much in this process; there's a few oz's of trapped coolant in the lower back corner. Pour this into the previously drained coolant.

11. Install is reverse of removal. Pour the drained coolant into the reservoir, with the coolant air bleed valve open, till coolant starts coming out (for model year 2010/2011). For later years the bleed valve has been deleted, but leaving a topmost coolant hose disconnected would likely serve the same purpose.

Note: not absolutely necessary, but be prepared to raise the front and remove the engine bay undercover. It "may" help with removal of EGR COOLER rear studs/nuts, or may become necessary to recover something dropped.

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can you describe the 'egr issues'? how many miles did you drive it in the year it took to happen again

 

Also, how clean did you manage to get it, in particular the cooler? It's very unofficial namesake (Toyota doesn't use the term cooler) is due to it's apparent function, to cool the exhaust gasses rushing through. If it's just partially cleared, it'll flow "better", but it's cooling ability will likely still be hampered.