Rough idle

[BritInNY]

Hi -

My 1989 Esprit Turbo (non-SE) has always idled rough, with the engine "hunting" between about 875-1050RPM. It doesn't stall but does run rough enough to shake the car. Once it's above idle it seems to run well. The car has 27,200 miles on it, the EBP valve and throttle jack have been removed.

I did a Freescan recording this afternoon - cold start, drive to fully warm up, then idle for 3-4 minutes. It wasn't hunting as badly as it has on occasion, but it was noticeable.

The .csv file is attached in case any of the experts here has a few minutes to take a look and maybe offer some thoughts on a potential cause. Any help would be very much appreciated.

Steve.

7-5-22-ColdStart-Drive-Idle.csv

[BritInNY]

Quick update: replaced the oxygen sensor (Bosch 13030) and IAC valve (Delco 217421 equivalent), did another reset of the ECU, and another drive with data logging.

The idle has definitely improved, though it's not yet smooth. Switching on the AC to boost idle to 1175 smooths things out to perfection - that alone is a massive improvement.

I should have mentioned before that the car recently had new fuel injectors (RC, supplied by JAE), ignition coils (MSD), and new plug leads (genuine Lotus). And a leakdown test showed <5% loss on all cylinders.

I'm rather at a loss. Any chance giving it some time to relearn might clear things up? New Freescan log is attached.

Steve.

new-o2-new-iac.csv

[Chillidoggy]

Did the problem start before or after the new parts were fitted?

[BritInNY]

Hi Ian - The problem was definitely there before the new parts - I've had the car for a couple of years and it's had the rough idle problem ever since I got it.

It spent some time in a local shop over the winter where they determined the coils were questionable and the injectors had poor spray pattern (cleaning didn't correct this, so I had them replaced). These changes did improve it a small amount.

So it's definitely getting better ... just not quite there yet!

Thanks -

Steve

[jonwat]

Does Freescan not display any error codes?

[BritInNY]

Hi John -

Nope! As poorly as it was originally running I expected some codes, but it has never thrown a single one. It seems perfectly happy - just idling a little rough.

Thanks -

Steve.

[jonwat]

Have you checked the camshafts are timed correctly, i.e not a tooth or two out of alignment?

[BritInNY]

Hi John -

Yep! I checked the timing shortly after getting the car just because of the idle characteristics, and while the car was in the shop I had them renew the timing belt and replace the exhaust cam pulley with a green dot pulley. All correctly timed (the mechanic was familiar with the pulley swap). Valve lash was also checked and found to be in-spec at the same time.

Your thoughts are going in the same direction as mine, which is encouraging!

Steve.

[AndyPG]

HT leads ok?

Possible air leak?

Throttle body balance?

Fuel pressure regulator?

How about a compression check or better still a leak down test?

Some folk have improved idle by replacing the IACV.

Andy.

[BritInNY]

Hi Andy -

Thanks for wading into this mystery!

HT leads are brand new (OEM Lotus). This made a small difference in conjunction with other changes that were made at the same time.

I've looked over the vacuum lines, but it's probably time to go through them again ... good thought!

I hadn't considered throttle body balance. Do you know if that would impact idle only?

Also wasn't thinking about the fuel pressure regulator as I figured fuel pressure issues would show up more under acceleration, but I'll add it to the list.

I had a leakdown test done late last year, with a result of <5% loss.

IACV was replaced yesterday (along with the O2 sensor) and this definitely had a positive impact. Idle now feels much better, though it's still fairly rough and hunts a bit rather than holding steady RPM. Idle is dead smooth with the AC on so the revs are around 1175.

Thanks for giving me a few ideas to chase!

Steve.

[AndyPG]

Hi Steve,

An air leak is a strong contender. Follow all of the pipes and check for damage and that there are no fittings without a hose connected.

The fuel pressure regulator is well worth changing, They are very cheap and easy to source and can certainly cause idle issues.

Might also be worth checking the inlet manifold gasket. Some use shaving foam or WD40 but it's a tricky little job.

Consider also that the Esprit idle can be a little lumpy. Some are very smooth but It has been well documented that there can be quite a bit of variation in idle quality from one engine to another.

Issues with throttle body balance will cause rough idle that improves as the throttles are opened towards the fast idle position. Check to see if the anti-tamper plugs are still in place. If they are gone, the balance will be well worth checking. If they are still in place, start by cleaning the inside of the chokes where a black film can build up around the butterflies. Some people discourage adjustment of the throttle balance saying it is factory set and shouldn't require adjustment. IMO they will need adjustment at some point during their lifetime but it is a job for the experienced and with the right equipment.

A reasonable check can be done with a 2ft length of 1/2" garden hose. Use it to listen inside each inlet while idling (plenum removed) The hiss of the inlet air draw should sound roughly the same in each inlet. If one (or two) are strangely different, there could be grounds to look into the matter further. If all of the inlets are hissing the same, probably move on to other checks. In my experience, some minor variation in balance has little effect on Esprit idle quality. This is probably due to the fact that the IACV port/rail links all of the inlets together allowing each to scavenge from one another.

Andy.

Edited July 11, 2022 by AndyPG

[BritInNY]

Andy ... thanks so much for the detail. The extra effort is very much recognised and appreciated. I'll start working through the hit list over the next week and report back with any findings.

This is the first and only Esprit I've been in so with a sample size of one there's been that nagging question of "just what is normal for these anyway?" I knew the initial characteristic definitely wasn't it. With the improvements I've already made I think it's getting close.

Thanks again!

Steve.

[BritInNY]

Time for a quick update ... took far longer than expected, but:

- Fuel pressure regulator has been changed (used a Tomco 21008, which is a PR103 clone - if anyone else trips over this and uses that part, make sure you also pick up three #10 x 32tpi 3/8" cap head screws ... different from the metric threads on the original). Unfortunately no change in idle.

- Inlet manifold gasket is intact. I have a smoke machine so hooked that up and showed no leaks.

- Throttle body adjustment has not been meddled with, and the hose trick sounds to my ear as if everything is well-balanced.

Next up: checking vacuum lines.

Steve.

[Elite 4.9]

One thing that will make a rough idle is if your spark plug leads are not getting all the juice to the plugs. This can still happen even with new leads. If there is any place where the wires are coming in  contact with some metal surface like the engine or another spark plug lead. Make sure your leads are not touching each other or any other part of your engine. This is more than likely a fuel or electrical problem.

atb,

Richard

 

[BritInNY]

Thanks Richard!

I had really dismissed the plug leads since they're new, but you're right: definitely worth looking at the routing at least. I shall add that to the to-do list!

Love your Elite, by the way!

Steve

[AndyPG]

Hi Steve,

I guess once the plugs and leads are eliminated, and all the other previously discussed items checked, you might be looking at injectors. Although your mileage is low, they are getting on a bit. Changed mine recently for RC's and made a world of difference. 80k miles on mine though.

Andy.

[jonwat]

8 hours ago, Elite 4.9 said:

One thing that will make a rough idle is if your spark plug leads are not getting all the juice to the plugs.

HT insulation breakdown would be most noticeable when the engine is under load as that's when the compression is greatest so increasing the resistance across the spark plug electrodes. If there's not noticeable hesitation when you accelerate away from lowish revs in a higher gear I'd suggest the ignition system is ok. I'd move on to checking the vacuum lines. 

[BritInNY]

Quote

Hi Steve,

I guess once the plugs and leads are eliminated, and all the other previously discussed items checked, you might be looking at injectors. Although your mileage is low, they are getting on a bit. Changed mine recently for RC's and made a world of difference. 80k miles on mine though.

Andy.

Thanks Andy ... The injectors were replaced over the winter with RC injectors from JAE ... I'm *hoping* they're not the problem. The originals were sent out for cleaning/servicing and they were deemed not salvageable - so your suggestion was definitely good!

Quote

HT insulation breakdown would be most noticeable when the engine is under load as that's when the compression is greatest so increasing the resistance across the spark plug electrodes. If there's not noticeable hesitation when you accelerate away from lowish revs in a higher gear I'd suggest the ignition system is ok. I'd move on to checking the vacuum lines. 

Thanks for wading in again John! There's no hesitation in that scenario. I'll still pay some attention to the plug wires while I'm chasing the vacuum lines, but I'll focus on the latter.

I appreciate all the thoughts and suggestions guys!

Steve.

[BritInNY]

This summer has just flown by ... too busy for my own good, but I did buy a fuel pressure gauge and got an interesting result: key on, fuel pump ran for a few seconds and pressure was around 32-35psi, then dropped rapidly.

So today I replaced the fuel pump, with really promising results. First, key-on yields 40psi and holds. I didn't bother starting it to watch the pressure - wanted to drive it! It's definitely idling a lot better, though still not *quite* there. Hoping to have a few minutes tomorrow to switch the fuel pressure regulator back to the original one to see if the pressure is a little higher, and if the problem is reduced more. The new pump was installed without the pulsation damper (immersion-rated fuel hose used to replace it).

For anyone else replacing the fuel pump, pick up a Kent Moore J-35731 wrench. I got one from ebay for just a few dollars and I wouldn't do the job without it - likely saved me a few hours of frustration.

I've found no problems with vacuum lines or with the plug leads, but I appreciate all the thought everyone's put into this for me so far.

Steve.

[BritInNY]

Just switched back to the original fuel pressure regulator, and key-on gives me 45psi, with a bleed-down to 35psi 15-20 seconds after the pump stops running. Not happy with the faster bleed-down, but starting and idling the pressure is rock-steady at 40psi.

I idled it up to temp (no time to drive tonight unfortunately) and when it dropped the idle down it did seem to be still more improved. Hopefully I'll get out for a drive this weekend and see how it's doing now.