Does a bad MAP sensor have long lasting effect on vehicle?

You have a bad #3 cylinder. Your mechanic should have told you why it's reading low (if he actually did a leak down test).
Before you do anything get that cylinder fixed.

IMO, I would just get a new long block.

 

Set the camera somewhere. I just want to hear it. If it can see the tach and speedo, that's a plus.

I do not see anything in this thread that indicates a clutch or driveline problem. I also don't see a sensor issue. You could possibly have something that is a little 'off' (but not wildly so), which can cause a fuel trim code. But it will not cause major running issues.

A valve timing issue (timing belt is not installed right) would probably set a CMP code and/or a VTEC code (manufacturer code, P1xxx). However, I didn't see you mention that the timing belt was recently done earlier. That may be the cause of your cylinder leakage. (bent valves if it broke, or if things were rotated too far during a routine belt change)

Again, I question your mechanic's abilities. A lot. If he did a leakdown test and found those numbers, he should have also attempted to locate where the leakage was. It's not hard. Open airbox as if replacing filter, and see if air can be heard coming through there (intake valve leakage). Then listen at the exhaust. Then take the oil cap off and listen for air escaping into the crankcase. It's going to be one of those.

If it does have a bad headgasket, it's not blown between cylinders. So it's probably between the cyl and a water jacket (so you could also possibly see coolant bubbling with compressed air hooked up to that #3 cyl). Or maybe an oil return.

It is not that hard to check for a plugged converter, also. The definitive check is to simply disconnect the exhaust and see if the engine runs normally. However, this can be harder to accomplish if there is a cat integrated into the exhaust manifold (not sure on that car). Can't exactly start the car with no manifold. But starting it with the pipe to the manifold disconnected won't hurt it.

I tried to respond to everything yesterday, since you're kind of all over the place on this. I may have just made it more confusing...again, I don't think this should be that hard a problem to diagnose for someone experienced with engine performance issues. Honda 4 cyls are just not that complicated.

Again, does the engine run bad at idle? If so, just record a startup...then walk around the car...pop the hood...rev the engine a bit (you can manipulate the throttle from the engine bay, it's a cable throttle). Build RPM's slowly...give it a couple quick revs...switch it up a little. Post results and I think I (and others) will have a better idea of what is occuring.

Right now it's hard to tell you where to go. If the leakdown test was done right, that's what needs to be investigated, I would say. It's not hard to pull plugs and you can rent a compression tester (or buy a half-decent one for like 25 bucks) if you're willing to do some diagnosis on your own. (edit: you need compressed air to definitively diagnose a belt valve, though.)

I'm happy to try and guide you down a proper diagnostic path. This forum has been devoid of good 'diagnose my car' threads recently and I'm bored...

 

By a vacuum gauge for less than $20, hook it up to one of the vacuum line, go to youtube, search for EricTheCarGuy and get the instructions on how to interpret the results to see if you have blocked exhaust. It is literally less than 10 minutes job.

Since your mechanic does not seem to know this, ditch him. He really does NOT understand the engine performance issues.

It is unfortunate that you are not much mechanically inclined but in these days if you have any engineering background or work with the computers day in and day out, it is certainly not beyond your abilities to do little bit of diagnostic work yourself.

Bottom line is that finding a talented *and* trustworthy mechanic is very very hard. If youtube is any indication of the pool of those mechanics, there are probably handful of them in the entire USA. Some of them are instructors in automotive schools and do consulting work for local shops (e.g. Paul Danner aka ScannerDanner on youtube) Extremely smart mechanics end up not turning wrenches but end up in higher paying fields.

Your mechanic is NOT talented that is for sure. I am with the previous poster. He knows a lot but unless OP wants to get his hands at least little dirty, it will be very frustrating for anybody else. There could be some local guys who might be willing to help OP but he does have to take some initiative. From my perspective, when somebody is not willing to even get the <$20 code reader, I tend to give up on them.

 

***, I forgot about the vac gauge test. I use them so little anymore.

OP, do what sontakke said. It's an easy, fairly conclusive way to check for exhaust restriction. Although a poorly-running engine will generate low vacuum in general...the gauge won't behave like it does with a blocked exhaust as you rev the engine, though.

 

If it only revs to 4k in neutral there's an obvious problem. ECU is definitely in limp mode to attempt to prevent you from grenading the engine. Please find a competent mechanic to figure out WTF is going on.

 

Some ecu do prevent revving car to the redline at idle. I do not know if your Civic has that protection. Get MS509 free shipped from Amazon for $49. This will give a good scanner which will let you look at lot more engine parameter even without opening the hood.

If I remember correctly, 22 inch hg of vacuum at sea level for a good healthy engine but do look up the youtube video for real details on how to determine if the exhaust is clogged or not. A decent MightyVac gauge runs less than $50.

With the scanner, testing TPS is trivial. And if scanner shows TPS operating correctly, a multimeter is NOT going to give you more data and you don't need multimeter to verify TPS operation if scanner has done the verification. Remember, if the car's computer says TPS is good, then it is good regardless of what you may find via multimeter.

If you give your location, somebody local might be willing to help you.

 

Vacuum at idle can be as low as maybe 16 inHg, but 20ish is a good mark.

If his engine is missing, though, vac tests might go out the window. I would really like to hear how the thing is running.

A consistent miss on one cylinder, and you can still probably spot a bad converter (as engine revs, you'll lose most of your vacuum well below WOT). Random missing, who knows. Also, if he has a miss due to a bad intake valve, that's gonna act extra-funky.

Again, video would be awesome. I could evaluate a video of a vac gauge much better than I can instruct someone to interpret results. It's more than just looking for a number, especially in this case. It's reading the fluctuations and how the gauge responds to changes in throttle.

Oh, and yeah, cutting spark at 4k is pretty common...on autos. He has a manual, so there shouldn't be any idle rev limit. Only input for the computer would be the clutch switch. It's called 'neutral safety,' but there's not going to be an actual 'the shifter is in neutral' input, obviously. Maybe some cars limit revs when the VSS reads zero, but I haven't observed it.

 

H22 ECU doesn't have that "feature"...unless it was added since mine was a '94 or so. It will not engage VTEC while in neutral though.

 

I once had a plugged/melted cat on a car and it would not go over 2200 RPM, it was just so laboured.

 

My coworkers Saturn suffered a similar fate. Symptoms were random stalling (like on the freeway) and lack of power. I don't think it threw any codes.

 

OK, it is a 2000 era Honda! Why didn't you say that before (I meant, why didn't I read that before?

You need one or more ignition coil! You are most likely running on 3 cylinder. You will have lots of engine vibration and it will tend to die or at least the rpm would go very low. You will be getting P030n codes. But one would think a mechanic would be smart enough to figure that out.

Now it is possible that because you ran the car like that you have now melted the catalytic converter and are running in to other issues too.

 

This was a 1987 Audi 4000. There were no codes thrown and there was an extreme loss of power due to the fact it would not go above 2500 rpm.

 

Usually it is the severe misfire which causes the cat to burn quickly. Many many cars drink oil without clogging the cat. Obviously it is not good for the health of the converter but blinking CEL (severe misfire) is extremely bad for the catalytic converter. If you had uncorrected misfire for a while then that is the explanation for the clogged cat not just the oil consumption.

 

Even though he solved his problem I'll just mention the the H22 never had coil packs, always a old school distributor.

 

wow! even in 2001 they were still using distributor? I sure hope they had finally fixed the problem with the distributor bushing which used to wear out in the older Honda causing a lot of ignition related problems. Drove me crazy on 83 Prelude until I found the hidden TSB and the new bushing from a trusted dealer technician. Dealer wanted to replace the whole distributor.

 

They switched to a bearing but inevitably it still wore out. But if the only real trouble spot is the distributor bearing, I think you're doing well as a car designer/manufacturer

The thing that was worse than the bearing failing with when they had the coil under the cap. That failed a lot faster than the bearing/bushing.

Small design flaws aside the '91 Accord my family had was bulletproof. When I swapped out the engine after 150k miles the only mechanical failures were an ignition coil and an alternator. I only swapped it because I wanted more power.

 

I think it allows for more accurate timing control but I really can't tell you why its superior.

Also, OP, its perfectly normal for that engine to use a decent amount of oil assuming you're driving it into the upper rev range. I would easily use at least a quart between changes. Nothing abnormal there. Sounds like your issues started partially due to lack of maintenance (as you pointed out already).

Oh, and don't bother replacing anything unless it failed. Thermostat would probably be a good idea since its over 10 years old at this point. I'm a bit surprised the radiator hasn't sprung a leak yet...stupid plastic tanks.

 

Preludes used to be better built cars. I drove mine (83) to the junkyard in 2000 after over 250K miles, original engine, original clutch, original transmission! I am almost certain that there would be quite a few Preludes still running with excess of 200K on them.

Honda is very conservative when it comes to latest technologies. They stuck with carburetors for many more years than other manufacturers. Similarly, they stayed with mechanical distributor and rotor far longer than others.

Starters, alternators, fuel pumps, wheel bearings etc are all wear items and as long as rest of the car is in good condition, should be replaced when needed. It is true that they can last 150-200K miles but by their very design, they will eventually wear out. What you want to do is to be able to recognize their impending failure before it happens and replace them at the first sign of trouble if you intend to keep the car.

Please contrast this with regular maintenance items such fluids, filters and belts ( and plugs rotor cap wires etc) which should be replaced on the schedule.