Just writing this guide to help people who have any power loss, or feeling of limp mode with their JTDM, most of the issues between the 1.9 and 2.4 seem to have similar causes and solutions.
When people suggest you start with the below list, they are not being difficult, but the majority of power loss issues people have are covered below. They are simple to check, and to go through , once they have looked at you can hopefully remove them as an issue before you start looking at 'more serious issues' that require more work, better DIY skills and tools.
One of the most common complaints to power loss with these engines is at low revs, with drivers complaining that there is no power, with the car picking up again at around 2-2,500rpm. Firstly, if you can get any fault codes read, will often help you determine the issue if it is not the usual suspects.
The most common causes for this are:
most common issue (90% plus), especially after 40,000miles (seems more cases are also raised during cold snaps!), normally diagnosed by a lack power lower down that seems to recover around 2,000rpm, when severe can stop the car starting, or in the early stages as a cough or stutter around 2,500rpm.
Can be easy and cheap to fix (and personally think cleaning it is a great preventative measure anyhow). If you want to determine if this is an issue, cut a piece of drinks can and place it between the EGR and inlet pipe (loosen the two bolts on top of the EGR, and slide it in underneath) (the guide below should make it clear where).
I think it is probably worth skipping this step and cleaning it anyway (see below).
If this is an issue, then first step is to try and give it a good clean, ( guide below). You often don't need to do the whole drilling thing, but just give the rest of it a clean. If the solenoid is still stuck, then you can pick up a new EGR for as little as £80.
(note on the 159, the engine cover just pulls off, no nuts or bolts involved).
Or watch this video, shows how easy it is.
How to Clean your EGR Valve - YouTube
To help prevent this issue in future, you should obviously clean it, then you can either blank off your EGR (which, without a new map will introduce a fault code), or restrict it with a restrictor plate (this is an official Fiat Mod, and can be purchased from the dealer, indepdent, or elsewhere),
Another sensor that is prone to getting clogged up, doesn't seem to cause major problems though, one hex bolt to remove and clean with carb cleaner, my car revved noticeably smoother after cleaning, it's just to the left of the EGR (there are some images lower on this pages courtesy of Alfadisiac):
Youtube video showing location and cleaning of the MAP
Another common one (though not always just at low rpm, often lack of power throughout the rev range), if your car is often used for city driving it is more likely. DPF blockage causes increased back pressure on the engine. Take it for an italian tune up on the motorway (30-40miles, at >2,500rpm), a dealer can do a forced regen, you can also get a bottle of WYnns DPF cleaner that allows the DPF to burn off soot at a lower temperature. Some drivers have been known to drill into their DPF, jet wash them, or remove them (with a remap(£300+) or a special dongle (£30) ).
If your turbo is not picking up, then you could have a leak in some of the boost pipes or the boost sensor could be dirty. This is a small black box on the front right (as you look at it) of the slam panel. Sometimes the pipes crack, or the sensor/ valve just gets dirty.
Cleaning the vacuum boost solenoid:
Check the pipes for a hissing noise, or a piece of toilet paper on a stick, especially if a mate can rev the engine).
Easy to diagnose, tends to show up first above 2,000rpm (across the range when it's fully dead), simply unplug the sensor, and should give 'normal' performance. Sometimes associated with a bit of smoke. You may be able to get away with just giving the sensor a bit of a clean (spray cleaner, avoid touching it). A faulty MAF can be linked to a failed EGR, as it can send the EGR crazy as it tries to compensate in conjunction with the MAP. It's a plug attached to a large black pipe onthe front right of the engine (left side when looking from the front).
Also only tends to be an issue when the car is warm, as the engine uses a default map up until it reaches operating temperature.
There is an issue with the plugs on the injector looms corroding, this is especially true on engines built before 07 (when the plug was changed). On the 1.9 this seems to be injector 3, and on the 2.4 injector 1 (but not limited to those!). This causes misfires and poor idling, often will bring up an error code. You might want to play round and check the connections.
There is a repair kit for it available from Vauxhall and autolusso etc; Partnumber 93189918 / catalogue number 62 86 769
For the 2.4 there is a software update, probably best to get that done first!
Swirl Valves / Intake manifold:
Again these can cause a loss of power low down (mainly due to EGR which soots them up). On older engines (with a metal manifold), you can see relatively clearly if one is sticking. Not so easy on the newer 'plastic' (black) manifold. A short term fix is to spray some carb cleaner in through the intake pipe which may, or may not loosen the deposits. This thread gives a little more info:
Battery Earth Lead
The strap that connects the battery to the ground (chassis) often comes lose or corrodes, this will cause poor idle, and often a few fault lights. The lead goes from the negative and connects to the chassis directly below the batter (often need to take the battery off to tighten). In an emergency, or to check, you can try connecting the battery to the engine/ chassis with any old jump lead.
You may well get this display on your dashboard, unless it's -5c or worse your car should be ok, only issue may be the car taking longer to start than normal. If you get this, it's normally one of four things: Failed Glow Plug (should read about 1 Ohm, also connect the plug across the battery, the tip only should glow after a second or two), Fuse blown (a 60a 'Midi' fuse, it's F73 and is the yellow one on top of the battery), or the glow plug control unit on the bulkhead. More details on all this: