I finally acquired a p1800ES (1973) about a month ago after quite some time admiring the P1800 series cars. I always liked Volvos and we do have a 1991 240 as well. It looks pretty decent in terms of rust and such since it is a California car, and for the interior it really only needs the front seats redone and eventually maybe the cracked dash. When I first got it and drove it it was running fairly well (I say this because I have no real way to compare it). The only thing I noticed from the start is that it had a slight hesitation from idle to acceleration and so I just drove it a bit more aggressively and that seemed to work well. It started right up and idled at around 900 when hot and all seemed pretty smooth.
After I bought it, I drove it for 45 minutes straight (including freeway speeds) while keeping an eye on the plethora of amazing gauges in the cockpit. Again all was well. Over the next few days I took it for a few rides along the coast etc, with the longest drive probably being around 2 hrs. Again, aside from the hesitations when driving it too cautiously it seemed to run fine. One of the symptoms of the hesitation would be on low acceleration (slight throttle) it would feel like it was in too high of a gear and jump/stutter/buck. With a decent amount of throttle/driving it slightly aggressively it seemed not to be a real issue.
As I like to fiddle with things and have been doing some mechanical work on my own cars for a while, I started to try and familiarize myself with the engine/system of this car and soon learned that (as many cars from the early era of fuel injection) there is A LOT to learn/troubleshoot. (And of course at the same time there is a lot of stuff that can go wrong or be out of whack and also many parts are hmmm lets say scarce and fickle). Of course the first few things I did was change the oil/filter, check all the fluids, pull the plugs to get an idea of how they look (all looked gray to brown which I felt like was decent, maybe on the lean side). I also changed the transmission oil just to see what I am working with. There are definitely some gaskets on the oil pan etc. that need to be addressed but after cleaning some of it and keeping an eye on any potential puddles, it doesn't seem to be an emergency.
After spending a few hours crawling google and various message boards I figured I should reset the throttle plate and throttle position switch and give it a good cleaning with some DeOxit D5 to try and start to set things up to spec and see if that helps the hesitation issues. After the cleaning I reset it according to the instructions (throttle plate ¼-1/2 turn open, TPS slightly more CCW after getting continuity on the bottom pins) and then went ahead and started the engine to see if anything had changed. The symptoms were still the same. I proceeded to clean it again and reset it once more just for good measure. I also wiggled most of the wires a bit and generally took a closer look at all the hoses and connections in the engine compartment. I noticed that a lot of the 'rubber boots' were falling apart and also some of the connector housings. Even though I could not see anything obviously 'wrong' it did concern me at the time. After fiddling with the TPS and throttle plate some more, I started the engine and I got a really high idle (like 2000rpm). I flicked the throttle a few times and got it to settle but some of the times it would just not settle back down.
During that time I also checked for a vacuum on the Auxiliary Air Valve when the engine was hot and realized that it was stuck open. (I found a used TPS and AAV on ebay and gave it a shot). I figured maybe the engine was running rich but pinching off the AAV didn't change anything. I unplugged the cold start valve and connected a pressure gauge to see where my fuel pressure was sitting. My gauge indicated 35 PSI so I adjusted the fuel pressure regulator down to slightly under 30 PSI (mind you it is a harbor freight one ).
In the meantime the engine started to run somewhat rough (almost like an 8 cylinder or in other words not on all cylinders and was shaking at times when idling but still at around 900RPM). It now also didn't start up on first crank any longer and just generally didn't sound as healthy as when I first started fiddling with it . At this point I am not even able to drive it any longer as it has no power and dies as soon as I use the accelerator. I basically had to stumble home relying on the TPS to trigger some injections and riding the clutch so I could make it around the block at 5 mph in first.
I did a lot more googling and message board crawling and started testing some of the sensors with my DVM. I sucked on the tube to the MAP sensor and checked the resistances which checked out as specified. The coolant temp sensor and air temp sensor seemed within range although the wiring of the coolant sensor looked very suspect. (On a side note: Is this the same reading I get on my temp gauge?). I haven't tested the thermo time switch (?name) yet but am not sure that it would really affect how the engine runs once it runs. By now I had ordered a tune up kit with plugs/wires/cap/rotor/points/condensor/coil (not sure what kind of ballast I should get). I did test it with another blue Bosch coil with no changes but will install the new Lucas coil. The pickup points at the distributor (21/12/22) tested out ok as far as I can tell. Next up will be checking some of the connections at the ECU (Bosch 02800000340). I also ordered a bunch of housings and pins from repro parts in germany to eventually redo the injection harness as mentioned in several posts.
After installing all the tune-up parts and testing the connections to the ECU (which all seem good) it still runs rough. I keep thinking it is something to do with fuel delivery. I disconnected the large fuel filter but it was wide open and the fuel looks extremely clean. When I first start it after the initial priming through the pump it revs up to 1000 rpm and sounds great then falls back and just kinda struggles and shakes from then on. The only way it seems that I can affect it is by flicking the throttle open to trigger the TPS pulses and even then I have to do it fairly fast in order to get a sustained rev. It also seems that it doesn't really matter whether the engine is hot or cold. I will have to check the injectors now that the seals arrived with all the parts I ordered. What really gets me is that it all started after I cleaned the TPS and reset the throttle plate, which of course could be a coincidence but it just doesn't make sense to me after reading up on the D-Jet system. At this point it seems that the only thing left is a couple (partially) clogged injectors? Can valves that need to get adjusted be at the root? Why would it 'all of a sudden' be so bad?
Any help/insight would be much appreciated. I apologize for this horrendously long post. I tried to write down as much information as I could.