I am not still fully satisfied with the idle even if I have done these:
I have replaced engine and transmission mounts, inlet manifold gasket, NGK spark plugs, leads, distributor cap and rotor, NGK Lambda sensor, engine belts, Bosch fuel pump, fuel pressure regulator, fuel and air filters, all the fuses, throttle position sensor, stepper motor, and coolant temperature sensor.
I have also cleaned the mass air flow assembly, throttle body, idle air valve and the earth connections, performed a vacuum check on the engine, a fuel pressure check and cylinder compression and leak-down tests, and tested voltages of the various sensors. Additionally, a specified company refurbished the fuel injectors.
Everything should be fine, and yes, the car drives well, but the idle could still be a bit better.
Hello Otto, I had a close look around my engine bay today and I donât have a connector similar to the one you have shown. The redundant connector in my car is a round shape like the black one shown above the one you have circled, it has two leads that emerge from the main loom near to the fuel rail.
What exactly is the problem with the idle ? Is it erratic, too fast or slow, how much is it surging ?
Casso, thanks for checking whether you have the blue connector.
The idle speed is correct, both cold and warm. The idle surges very little. I can feel some vibration in the cabin. The idle is not bad at all, but just not perfect.
Since I have pretty much checked and/or renewed everything, next I may experiment with a different ECU. My current ECU has been remanufactured in June 1997. It has such a marking.
I tried an another ECU. It did not have any effect on the idle. Now I am running out of ideas what to do / check next. I have done pretty much everything I can think of.
The car runs well. So, maybe an imperfect idle is just a property. As said before, the idle speed is correct, both cold and warm, but the idle surges a little. I can feel some vibration in the cabin. The idle is not too bad, but just not perfect.
A rough idle is one of the toughest things to troubleshoot because everything has to work properly.
Your thread has gotten too long to reread so at the risk of repeating things that have already been said if I were you I would check the basics.
Mechanical ⌠compression check (leak down check even better)
Fuel ⌠injectors, filter, rail pressure.
Electrical ⌠coil, plugs, wires, rotor and cap.
Barring a mechanical problem your rough idle is being caused by a misfire or vacuum leak.
My advice would be to have your engine checked by a pro with a professional digital analyzer (these replaced the old oscilloscopes). It will tell you whatâs going on dynamically (with the engine running)
This is done with modern cars through the OBD2 port utilizing specialized equipment.
The data will show you if the misfire is only on one one cylinder or âtravelingâ across different cylinders. Knowing this will help you zero in on the cause of the problem(s).
I have done compression, leak down, vacuum, and fuel pressure tests. The values were good. I have also renewed the fuel pump, fuel filter, and fuel pressure regulator. Additionally, the injectors were refurbished by a speliazed firm, since new injectors are not available. Moreover, I have renewed plugs, wires, rotor, and cap. I have renewed the stepper motor, too. Furthermore, I have checked the voltages of the various sensors and they were proper. I have renewed the coolant temperature sensor just to be sure. Even the inlet manifold gasket has been changed. In addition, I have cleaned the throttle body.
Your idea to check the engine with a professional digital analyzer is relevant!
Actually, the surging is worse when the engine is cold. When the engine is warm the idle is much better, but I can still feel slight vibration in the cabin, and yes, I have renewed the engine and transmission mounts.
When you replaced the stepper motor did you clean the idle air control valve? It can gunk up. I sprayed mine with carbie cleaner and a lot of muck came out. Just be careful that none gets in the electrical part.
Youâve certainly done your homework and paid your dues on this problem.
After accomplishing a compression AND a leak down test with good results you can eliminate an internal mechanical problem. Since that would be the most expensive repair thatâs great news.
Now if itâs not a vacuum leak (did you do a smoke test) it almost has to be a misfire. So the problem is finding out which cylinder(s) are involved.
Take my advise and have a dynamic engine analysis done. Look at the bright side, with a 33 year old car all the things youâve replaced (even though it hasnât been the cause of your problem) is still money well spent.
⌠an âOh by the wayâ âŚ
I just replaced my steering rack and after crawling around under the car covered with P/S fluid I said to myself, âIs this 3 decade old love affair still really worth itâ ? But the next morning when my wife and I
jumped in the Jag and went out for breakfast, the answer was a definite ⌠âYesâ
Gary,
Yes, I cleaned the idle air valve. By the way, the lambda sensor has been renewed as well. Some of you may remember that I had difficulties removing the old sensor in fall 2020.
Dennis,
I did not perform a smoke test, but I followed the vacuum test instructions in the Haynes manual and used a vacuum gauge.
I am happy to hear that you finally solved the steering rack leakage problem! Maybe you remember I replaced the seals (around 20) of my Adwest rack a year ago and luckily havenât had leaks ever since.
I agree with you that the relationship with these cars is invaluable.
Since youâve done everything else I would also suggest doing a smoke test of your intake system. It doesnât take much of a vaccum leak to produce a rough idle. I made the smoke machine (the tall one) in this video and it worked very well.
The odds are that a vacuum leak may not be your problem, but for a small investment in time and money itâs one more thing you can eliminate.
Since I am a part-time musician I have access to an entertainment fog machine.
The diameter of the grille of the machine is around 60 mm. My plan is to clamp a 60 mm hose around the grille with a hose clamp and then use thinner adapter hoses to finally attach the hose to the nipple next to the fuel pressure regulator in the intake manifold.
How about using a plastic funnel. You can cut it down so the large end fits over the smoke machine grill and secure it in place with duct tape. Then slide the plastic tubing over the small end of the funnel and tape it in place. I donât think the pressure is that high but if you need to you can still use the hose clamp to hold the tape around the grill.
The last update of this thread was in early May. The biggest project I have done after that was the renewal of the side vents behind the rear bumper and fixing the plate below the black trim that sits at the bottom of the boot lip. The plate has 3 screws and water will accumulate below there and enter to the boot via the screw holes.
I got the last side vent from Jaguar Classic Parts. Luckily, I found another one from Spain.
As I have reported in spring 2021 I renovated the center console wood trims by gluing 0.6 mm thick walnut veneer to the frames. That worked quite nicely. However, I recently got nice original wood trims.
Last week I renewed the transmission filter and seal. I could drain out four litres of old fluid. I poured four litres of new fluid and I will replace another four litres in the near future. Next I am about to change the right rear hub since one of the studs is broken.
The AC and steering rack (I replaced all the seals of the Adwest rack in early 2021) have functioned nicely.
I replaced the right rear hub on Monday. It was relatively easy. However, at first it was difficult to get the new hub fully into the carrier. The trick was to guide the drive shaft with left hand and push the hub with right hand simultaneously. When removing the old hub it was necessary to use a two leg puller.
As said before, the idle speed is correct, both cold and warm, but the idle surges a little. I can feel some vibration in the cabin. The idle is not too bad, but just not perfect.
