Recently had a major (30k) service and since then have had some variable hesitation on gentle acceleration.

Generally, it's when in traffic or town (30mph) driving and when feeding in the throttle it hesitates, hesitates hesitates then, at some point, off it goes. It's like flicking a switch, trouble is the throttle will then be further down than you would normally expect so acceleration is quite rapid.

I detect no such hesitation when pushing on at higher speeds.

I think I know what is causing it but does anyone have any suggestions?

 

I had something similar and it improved significantly when I checked my spark plugs I found them to be only hand tight; I fitted them myself so I assume they'd worked loose over time. I still get a tiny hiccup at around 1200rpm and again around 2500rpm if I accelerate gently but it's not all the time.

Also worth checking the coilpacks are in good nick. Earthing is also a problem with these cars when they are getting on and I'll be fitting a grounding kit when I fit the new turbo

 

+1 - had the same issue and my plugs needed replacing.
I've also had a similar problem where one of the coil packs wasn't tightened properly and had popped off the plug, resulting in the car going into limp mode and running like a tractor (and sounding like one too)!

Jon's advice is spot on.

 

I was going to check my plugs again today after the oil change but I couldn't be bothered - she's coming apart soon for a new turbo, TGV delete, painted inlet and to sort the leaking rocker gasket so access will be easier then

 

If it was loose connections or dodgy coilpacks wouldn't the hesitation continue into higher speed driving?

 

Nope, I've had it with a loose coilpack before and the higher revs assist in the current arcing across the gap and it runs better at higher revs

 

OK, that's interesting.

My theory was that NGK ILFR7H plugs were installed and I think the standard plugs are 6s so I was assuming the plugs were too cold and "oiling up" when driving slowly but cleared when going faster - any thoughts?

I know the plugs are a pig to get at; those of you who have replaced them yourselves do you need any special tools or just small hands?

 

I've also got this issue and so far I have done maf,boost solenoid,plugs, turbo, air filter, butterfly delete valves, Waldron 255, uppipe, downpipe, full decat, remap, checked all accessable earths, sti pinks and I also had to press gas more than normal only to be greeted by a huge kick up the *** when it decides to go. It almost feels like the turbo goes from nothing to 1.3bar instantly not a smooth but powerful surge as it should be but more like being crashed into the back of. On low to half throttle it feels like its cutting in and out of boost but anything past that and it's off like a rocket. It all seems like its electrical rather than mechanical, I'm thinking of changing the coil packs so I'll keep all posted. Good luck mate hope you sort it soon, please post results if you manage to find the root of the problem.

 

I have heard of an issue with a hesitation when the boost comes in - it can be mapped out apparently. That would make sense with my 2500rpm issue.

As for changing plugs, you'll need a 10mm offset ring spanner to get to the coilpacks and a 2" long extension on a 1/4" ratchet for the plugs. You will need to remove the airbox and washer bottle (making sure you don't clamp the bottom hose when you refit it). Some people remove the battery to but I find it unnecessary. Then it's just patience as you won't turn the nuts/plugs very fast. Once the coilpack nuts and plugs are loose enough it's quicker to get you hands in and spin the nut/2" extension by hand

 

Same as mate - first time I changed my plugs I removed the battery, second time I didn't bother and it was SOOOO much easier having done it before.
First time took me about 3 hours!
Second time took me about 45 minutes to do all 4

P.S. To the OP - ensure your plugs are gapped correctly. For unmodified cars, around 0.7mm, for elevated boost, 0.65mm or even 0.6mm if very aggressive.
If the car's not modified, try 6's instead of 7's.
If you're running in the 300+ category, 7's are probably ok.

 

Also check none of the connectors to injectors are loose, I've had this cause hesitation like yours after a service

 

Car originally had PPP installed but last year had new head gaskets, revised turbo and forged pistons followed by a JGM remap running at just under 330.

Thanks for your responses and advice - a few things to check although somewhat frustrating after a service.

 

7's are fine then - ran them on my old WRX at 320bhp with no problem - Simon mapped that too.

 

This Sounds Like Mine Too. Did You Resolve This In The End?