Ok so I had a chance to look at the car today and covered lots of tests. I did not learn a lot, as my understanding is poor, so still need help with this. All tests are run on a warm engine with the airbox off (like in the first picture - but with the vacuum line fully connected).
Summary:
- Loads of testing has been undertaken
- Brake booster seems ok but there appears to be a vacuum leak somewhere on that line. However, even when this is isolated the car idles high
- I have not found unusual spikes in any of the telemetry data though the idle control valve seems to be behaving differently
- Swapping lambda sensors did not help and I could not find an air leak near the throttle body or inlet manifold
- Car is driving notably well but idle remains high (1,500 to 2,000 RPM when engine hot)
Thanks for all the help but please only read beyond this if you are a glutton for punishment!!!!
These are the detailed steps I took:
1) Check Air Leak on Vacuum Line to Brake Booster:
• I ran the engine and pumped the brake, the engine rev’ed/stalled. Then I disconnected the vacuum line to the brake booster at the inlet manifold and blocked the port. Pumping the brake did not rev/stall the engine. Note in all subsequent tests the vacuum line has been reconnected
• Then I checked the brake booster and it passed all steps and seemed really good to me. The test is here:
Test
• I checked the behaviour more carefully and I did notice that when the brake is pushed in the engine rpm changes slightly for a moment, when it is held depressed there is no change in engine rpm and when it is released it revs / increased RPM more significantly but again momentarily. So the changes in RPM only occur momentarily when the brake is moved and not when it is held. This made me wonder is this normal behaviour – as cycling the brake is not typical?
• Even when the vacuum line was disconnected and the port blocked the engine was still idling high. Due to this I did not look further at the booster side as I felt there was still a problem somewhere else.
Questions:
Q1.1: Is cycling the brake (say every second or twice a second) leading to engine reving actually normal behaviour?
Q1.2: As the engine idles high when the vacuum line is removed, and the port to the inlet manifold blocked, am I right in assuming that there is an idle issue somewhere else anyway?
2) Check Vacuum Leak – Inlet Manifold and Breather Pipe:
• I really tried to find something but struggled to get anything. I sprayed "easy start" all over the places of interest and nothing. Later I tried WD40 with a long spray nozzle and sprayed it vertically down the manifold interface with the cylinders using the four bolts as a spatial reference. Could not find sign of a leak, e.g., spray affecting engine tone
• I removed the breather pipe (see below). I blocked two ends with my fingers and blew in the remaining end until I was close to passing out. Nothing, no leaks evident.
Questions:
Q2.1: Anywhere else I should look for a leak? I will try the evap circuit when I can, I have not gotten to it yet.
3) Check Throttle Pedal and Position Sensor on throttle body:
• I had a good look at the throttle pedal and, as you probably all know, there is no electrical connection or sensors, just a physical throttle cable that runs through the bulkhead to the engine bay and over to the throttle body. The white plastic "hex cog" part pulls the cable
• I removed the fault code to see how long before it reappears!
4) Swap O2 Sensors:
• So I found a new lambda sensor in the garage and fitted it in the pre-cat position. I then ran the engine and then put the old pre-cat sensor in the post-cat place and ran it again. The high idle was still present in all of these tests. The two used sensor are shown below.
5) Logged and Review Some Longer Run Sensor Data:
• I was looking for spikes or anomalies, which are hard to find for my acquisition rate and did not find anything in: Coolant temperature data or throttle position data (see below for TPS data for an engine off test, but similar for engine on). Also kept an eye on others and found nothing that stood out to me.
6) Some General Checks:
• I ran the engine and monitored the data. I noticed that I could not hear a click from the idle control valve as I had before so I looked at the data. The expected behaviour is not evident, i.e., click from throttle body followed by revs dropping and inlet pressure increasing! I show this below where on top I have a prior measurement (I expected this again) but below is the most recent one (I got this one) - I do not see the idle control valve impact and could not hear it click?
• I was told that the middle two spark plugs were connected to the same coil pack I had a look and this is correct! Interesting. In looking at this I noticed that the harnessing for this coil pack was damaged so I wrapped insulating tape around it just in case. This harness sits over the engine and the outer black protection was embrittled and flaking off. The wires looked ok.
Before Image:
After picture:
• I have been driving the car since the latest changes and it is driving smoothly and I have not been able to provoke any judder yet. Maybe it will appear but I would have expected it to have occurred a number of times over the distance I drove. However idle remains high
• I have not checked the evap circuit as I need to find out more about this before I take it on
P.S. if you have read this far you have truly earned my respect!