What is an HT lead ?
Have you put some silicon spray on the rubber seal of where the hatch glass seals to the B pillar and also where it sits on the back of hatch ?
You should check all ground connections as clean and tight, even the ground splice packs, do a search on forum as I
did a long write-up of where each ground and pack are.
The controllers will not work correctly if weak grounds or battery is faulty
Should read with meter at around 12.7 volts with IGN key off and the controllers in sleep mode
When at idle should be around 14.3 volts
Any auto parts store should be able to do a battery load test while the battery is in the car and also test the alternator
Any auto store would sell a special dye and a special light, you put the dye in the oil and then use the light will show where
the dye is coming out of.
As to MAP sensor, it is tight, but I can slip my hand there to work on it.
Right next to it is a small 1/8th vacuum hose, that supplies vacuum to the HVAC doors in the cabin
If the doors do not work or are slow in changing state then that hose could be leaking, and any vacuum leak will affect MAP output
Again, would be easy to solve MAP issue with a OBD-II scanner.
Not sure how close you would be,
but Keith of Eurovettes recently bought a full functional OBD-II scanner and a PCM/TCM tuning flash tool I have been working with him on that
Maybe link up with him ?
You or someone needs to follow the debug info I posted above to solve MAP but start with good battery, grounds and that wiring pins
of MAP sensor and wiring connector are clean
Lastly, check below battery towards the right firewall, some GM batteries leaked acid that dripped down to where the PCM is and
caused wiring damage.
There is a small section of lower right innerfender that has some small screws, taking that out you then would see the PCM, TAC and
the vacuum router to see if any acid damage there
My 1999 C5 which I have owned for like 23 years has never had an oil leak and I work on countless C5s and not had oil leaks
About where is the leak ?
Have you checked the PCV hosing from right head to rear of left head ?
Maybe around where MAP plugs in and oil showing there and also oil getting into MAP sensor will cause problems
When car not used it MUST be on a battery tender as not only small current draw but also degrades battery
My 1999 has been on a tender for 23 years and only changed battery once.
A wire set basically... being in the bike trade, its known as a HT lead.
I found a well branded silicone set on Amazon for not a lot of money so got them ordered, I just have a 2-3 week wait for them to arrive.
I'm not worried about the MAP sensor fault at all if I'm honest. this problem only occurred as my battery is really weak! As stated in my previous post, the code clears instantly and the car drives absolutely perfect with no issues regarding idling, revving and driving. When I turn the car off and come back to it, it will do it again. Again, the code clears fine and the car drives fine. My ACDELCO battery has a little sight glass on the top to show the batteries condition. Green for Good, Black for Weak, White for Knackered. It was on the car when I bought it so that has been on since god knows when? I bought the car from Japan (Genuine GM Japan model) so who knows how old the battery is!!! It has however always showed Green for Good and cranked effortless all year. After this recent cold snap we had, it now shows Black for Weak. Not the only vehicles that has suffered with the weather the way it was... I also had to put a brand new battery on my Lexus SC430, Subaru Impreza and 2 of my motorcycles as the weather had killed them all off. Given that this doesn't get used much AND taking in to account that the battery is on the side that the car points away from the house... it all adds up to why the battery has finally snuffed it. So a new one on order after the new year, hopefully that will sort my 'Check Engine' light for the P0107 MAP code
One step at a time on that fault.
As for the oil leak, it's been a curse for me with this car since I bought it!
I bought it knowing it had a gearbox fluid leak where the cooler pipes connect the front half of the pipes to the rear half. I sorted that by simply draining the gearbox fluid when I serviced it, took the 2 joints apart, cleaned them and applied Loctite 542 (seals threads in low pressure hydraulics, resistant between -55C to 150C) and then resumed the service. Been fine since and no issues (done in May of this year).
I always had a smell of oil coming from under the motor after a drive which I couldn't pin point for months, until then I had quite a serious oil leak from the rocker covers that dripped directly on to the exhaust manifolds on both sides! New rocker cover seals sorted that out which included the seals for the bolts also. That's been fine and no issues since (done at the end of September of this year).
Then I had another major oil leak from the front of the motor which was running right under the sump. Too big a job for me at home and much to time consuming to use a ramp at my cousins garage. So I had to send the car to PartsUSA who investigated it and found my front timing cover had split! so they fixed that, new seals also, new water pump, SUMMIT harmonic balancer, crank pinned and so on because why not... well known issues as we all know. That's sorted and no issues there (done in October of this year).
Now however, I still have a whiff of oil after a drive and on the right hand side of the motor, at the front of the block. I get a pool of oil sat on the little square part on the block located behind the air con pump, under the front of the exhaust manifold if that makes sense? I can't locate it AT ALL!!! I can't find any evidence of it running down the block anywhere... It just has a little bit of a wet shine on the corner of the base gasket and pools on that little square piece I'm trying to explain. I have no loss of oil on the dipstick and I wipe it clean, go for a drive... back again
I've even had my inspection camera all the way round there but to no avail. I even stood on my driveway for nearly an hour watching the car to see if I could see it leak AND IT DIDN'T!!! So this is obviously when the car is revving and/or in motion, that it shows its presence.
I also noticed a few days ago also when my car was running on the driveway, 2 small dots of oil on the floor from the BACK of the motor somewhere
So I need to inspect that also amongst all of this
As for the squeak, it wasn't there when I bought it. It slowly crept in over time.
Over a few months it got gradually worse and worse to the point where I heard it outside (with the targa off), as much as inside (with the targa on).
So after nearly writing the car off around the same time my squeak became unbearable, this is because I had to brake REALLY HARD thanks to an idiot pulling out on me on a national speed limit road, the brakes boilt over from just braking that once and I very nearly couldn't stop in time for the upcoming roundabout! Anyway, I knew I had to rebleed my brakes so prepared myself with new MOOG drop links and ARB D bushes front & rear.
I stripped every corner, cleaned, regreased, refitted and rebled all the brakes, changing the drop links and ARB bushes as I went along. Brakes much stronger and more efficient. the squeak still continued.
I then removed the ARB D bushes again and absolutely caked them in copper slip, but the squeak still continued.
I then knocked my exhaust tail pipe by accident when cleaning my car and it squeaked! so I found that it was in the rear right rubber hanger it was squeaking from. sorted that but the squeak still continued.
I then developed an almighty creaking in the cabin which turned out to be a loose torx bolt for the targa top. fixed that and wondered if it was the boot lid bolts causing the same issue? so I stripped them all, cleaned them and refitted them, the squeak still continued.
I've adjusted the boot height rubbers thinking the boot lid was rubbing against the body, the squeak still continued.
By this point, I have noticed the squeak is much more noticeable INSIDE the rear of the car on both sides, around head height.
I'm now on to believing it is interior related... I'm going to remove the boot gas struts to see if it stops. If not then I'll have to just start removing trim until I can hopefully find the issue OR points me in a better direction at least.
So I can only apologise for venting but you can see why I really am at my wits end with the car.
I really looked up to it as a child and have since wanted one.
As added fuel on the fire, my mum passed away horrifically last year, I found her as well and have since been suffering with severe PTSD and depression. However, she was kind enough to leave me a secret trust fund that a solicitor contacted me about after she had passed, with instruction to go and purchase a Corvette. She knew how much I loved the C5 Targa. So understandably, I'm absolutely heart broken that I'm having to deal with all of this, when I just want to be driving around with the roof off saying ''thanks Mum''
a full shame as I had big plans to do trips next year including a run through Europe... now I just can't trust it because I can't even get 30 miles from my house without the NEXT episode of let downs! 
