Help! My car stumbles as if it wants to stall when accelerating slightly from a stop and it also surges when in motion sometimes especially when my leg is off the accelerator pedal and I am descending a slope. There's no vacuum leak present, no hard starting in the morning, it vibrates gently when at stop in traffic, there is considerable power loss. Spark plugs are brand new bosch iridium and ignition coils are brand new too, injectors were serviced recently, maf sensor was also cleaned with a crc maf sensor cleaner and throttle body too was cleaned.
Car details: 2007 Mazda 6i 2.3L 4cylinder

With all you have done you need to check the fuel pressure if it is still within the recommended pressure working range and the fuel pressure regulator.
Also u need to change ur air filter if it is dirty.
Still try to look for any vacuum leak in the system.
If your check light is ON try scan as well.

I have changed d air filter recently and I also changed d pcv valve, pcv hose, and all intake manifold and egr gaskets. i also cleaned d egr valve and intake manifold before reinstalling them. There is no check engine light on. I did a scan but no code.

Series of test needs to be carried out on that vehicle of yours. A quick question here what type of scan did you run?? Was a live data stream carried out to check all modules of the vehicle. Did you carry out a fuel pressing test?

Could you refer me to where I could do a good affordable check on the car? Preferably, around ikeja or near ikeja. Thanks!

kenmaro: Could you refer me to where I could do a good affordable check on the car? Preferably, around ikeja or near ikeja. Thanks!

Call Chikaodi 07042076444 07031909669, 08023288111. Tell him you are calling from nairaland, he can come and meet you wherever you want

kenmaro: Could you refer me to where I could do a good affordable check on the car? Preferably, around ikeja or near ikeja. Thfanks!

Go to Navy yard at Ile Zik and ask for Jaguar. He is good at what hw does and has a proper diagnostic machine

do a cylinder drop test

Basically remove the wire to each coil one at a time you will notice a change in the engine sound then reconnect it, if your engine does not change then you know which cylinder is not working do that by yourself first then let us know if there was any difference in ant cylinder

I have done that already and all cylinders are ok.

kenmaro: I have done that already and all cylinders are ok.

Do a compression test on all cylinders, check timing marks.

Now, this sounds like a low fuel pressure symptom.

If you can't find where to test the fuel pressure with a proper tool, I would suggest you swap in another fuel pump and see what happens. Your mechanic should be able to get a pump to do the test.

But before that, check and make sure the fuel line(s) under the car is not damaged. Because a bent fuel line will reduce the fuel pressure.

Failing or faulty MAF could do that, likewise weak upstream sensor. But I would start with the fuel pressure, if I were you.

Ikenna

By the way can you explain when it started and what type of service was done just prior to the stumbling

sultaan: By the way can you explain when it started and what type of service was done just prior to the stumbling

Prior to this, the services done was intake manifold gasket change and I cleaned d egr valve and reinstall with a new oem gasket, Also, there was a worn ac valve seal which was replaced and d AC gas was flushed and refilled too.