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Do you have any diagnostic trouble codes for misfires, such as P0300 or P0301-P0306?
No codes unfortunately.
you could buy just one Diamond coil and swap it in for each coil one at a time to see if the running improves, and buy more Diamond coils only if necessary.
Hmm was thinking that was a better solution, even if there wasn't a huge difference a spare will definitely come in handy. To be honest it would probably be good money spent to get the cover refurbished, since its hard to find better condition ones 2nd hand.
the strength of the coil and should range in the 30,00o volts , but then they fail as they are heated up in on car driving practice .
The three symptoms are rough idle, infrequent stutters when sat in drive at stoplights, and rpm drop when coming to a complete stop. Its independent of temperature as far as I can tell.
When I start the car from cold its smooth, but then as the IACV drops the idle it stages it gets progressively worse, and more jittery if idling for several minutes at a time. When I had the car scanned for codes, he said the IACV is working, as well as the O2 sensors, so its sneaky vacuum leak, fuel pressure, coils, bad ground somewhere or internal valve issue.
As for the sneaky vacuum leak, cap off the air filter with some saran wrap, and blow some cigar smoke into the camshaft hose. You might notice where the leak is that way.
I found a small leak in the IACV itself. There is an o-ring that was bad.
I found a small leak in the IACV itself. There is an o-ring that was bad.
Interestingly enough, when attempting and failing to do an oil change today (Filter and nut far too tight), I thought id check the IACV, and to my surprise there isnt an O ring in place.
The paper gasket is in a pretty sorry state too. Perhaps its best to use this opportunity to replace it with a new one, as its another thing ticked off the list then. I just dont want the new one to cause new problems. Is a simple swap ok for a UK car? no adaptation or anything like that?
IAC valve since it is a commanded to position valve and has no feedback sensor on it's postion to the ECU should not need a ECU reorientation from what I understand .
Took me 7 days on the drain plug with some penetrating oil and a heat gun with 2 wrenches hooked into each other for more leverage .
I kept a souvenir oil sample . probably never changed .
Last edited by Lady Penelope; 05-01-2018 at 11:37 AM.
That makes sense to me. My concern came from other users who claim that a software reset is needed as the IACV and TPS are "paired" in some way. I guess that the TPS adapts to an IACV that fails slowly over time. When I had my cars codes read, David Marks mentioned that my throttle position percentage was fine, and so surely my voltage at idle will be correct? Hopefully this means that I wont get any high idle issues if I replace it.
Took me 7 days on the drain plug with some penetrating oil and a heat gun with 2 wrenches hooked into each other for more leverage .
Used a breaker bar last time, only been a year & 7000 miles since the last oil change, cant figure out why they have got so tight since then!
The IAV valve has a stepper motor that has a scheduled varying amound of opening sequence commanded by the ECU and is not a simple open and close hence the 4 wires
From how it should be designed in schedule as you slam the throttle closed to prevent stalling the IAV should be wide open and as the RPMs settles down the IAC will close up the match the idle speed The IAC position adapts to the TPS position over the short spool down time period Vs. a long period calibration to each other .
Last edited by Lady Penelope; 05-01-2018 at 11:56 AM.
Interestingly enough, when attempting and failing to do an oil change today (Filter and nut far too tight), I thought id check the IACV, and to my surprise there isnt an O ring in place.
The paper gasket is in a pretty sorry state too. Perhaps its best to use this opportunity to replace it with a new one, as its another thing ticked off the list then. I just dont want the new one to cause new problems. Is a simple swap ok for a UK car? no adaptation or anything like that?
its a metal gasket, can be bought separately, and this is what 5/8” gasket looks like
Put on a new pulley and belts today, managed to get the car up on the ramp and got it up to 70 mph indicated, had my brother and his mate looking underneath at the time, said that the propshaft was running true but the drives side halfshaft seems to be vibrating as its got a slight bend in it. I could see the free wheel jiggling up and down. Does this seem consistent with a vibration from 65mph felt mostly through the seat? Also we found the source of my ac leak, ac compressor is full of holes, happy to get a genuine denso replacement, but Id like peoples opinions on these other brand ones that are supposedly the same, are they any good?
Im not expert on rebuilding things like compressors, happy just to get another one with a warranty on it, was just curious if anyone else had done this either with a new oem or an other brand one. I could actually hear it hissing faintly the other day by the compressor, cant isolate it to a specific bit, just the general area, lots of AC hissing recently so looks like another 1kg of refrigerant gone.
Ordered a good used halfshaft, and two new UJs, il trust my brother and hopefully he is right on this one, not bad at £70 for the lot. Did some refurbishing of the two relay brackets on the RHS engine bay, wire wheel and a gloss black rust to paint can. Look much better than before, although because the metal is so thin, once the surface rust comes the panel is compromised and therefore you cant remove material and replace with filler. Cleaned up the ground stud in that area as well, although I cant remember what circuits use it off the top of my head.
Bought a new IACV valve for the hell of it, tried it on the car, expecting a high idle, as the plunger on the new one comes fully retracted, and it started on 1800rpm and stayed there, which I thought was odd since when I removed the new valve the plunger had adjusted to the same length as the old one.. hmm.
In the meantime ive transferred the new o-ring, gasket and screws and kept the old one on for now. Im thinking I put the o-ring and metal washer the wrong way round, and so created a vacuum leak which is why it stayed at high idle.
I had it like
o-ring-->washer-->gasket
the first try, then switched to
washer-->o-ring-->gasket
I haven't bought the IACV to cure the rough idle, more to stop the rpm dips and occasional stalling when switching to reverse with full lock on.
Yeah I got the washer part when I noticed that it was stuck into the throttle body when I remove the old IACV. Il swap the o-ring and gasket round at some point this week. Seems to have helped some anyway, not had any stumbles when moving from drive to reverse, although im still using the old IACV so im not sure whats changed to make a difference!
Il have to try the new valve again too, as its extended to the same length as the original IACV, so I cant see why its not just a simple swap over.
Been thinking though, if my idle is normal, which it is, then surely I cant possibly have a vacuum leak, and therefore can eliminate it as a cause of the rough idle?
Been busy recently, fitted a new IACV, with not much issue, hasn't affected the idle. Car seems to stumble less frequently when moving between drive and reverse. Bought a genuine coil from SNG Barratts UK, tried it in each position for a few minutes of idling, like Vee suggested, and no change for any, so I guess that rules out a coil issue?
Not really sure what to try now, don't want to just keep replacing parts, might just give up and take it to a specialist.
Might inspect 4 specific sockets on the black ECU connector . If one of these sockets is bad you would be missing a leg driving the IAC valve to it's proper position . Start on reply # 46
Il have a look at the ECU, ive felt around for any damp in that area and its all bone dry, but perhaps definitively removing the sockets and inspecting is the best way to go.
Can the anti tamper screws be removed by drilling out? I have a dremel if not. Also when I disconnect the sockets I should have the battery negative disconnected yes?
Also I should mention Lady P, since I know you talk about the 2 ECU plugs in the engine bay, Ive tried to inspect the sockets, but im unable to actually separate them, which makes me worry about corrosion.
Probably nothing but I get no change at idle when removing and plugging the vacuum line going to the fuel pressure regulator, but ive read up and people say there shouldnt really be any change, its more if the FPR has a failed diaphragm that the issues start.
Is there a safe spray/lubricant to try and coax them apart? Also couldn't a weak camshaft position sensor be causing most of my issues? A quick google search returns:
"If your vehicle idles roughly, stalls frequently, has a drop in engine power, stumbles frequently, has reduced gas mileage, or accelerates slowly, these are all signs your camshaft position sensor could be failing."
Fair enough is generic and not vehicle specific but worth looking into surely? Although irritating that its NLA from Jag nor are there aftermarket replacements available.
04-30-2018, 02:05 PM
