Help! 1995 NA Idle/Power Issue

[kilgh]

Reaching out to the great minds here! My beast is causing me no end of issues that no mechanic is having luck with. Story so far:

Car water pump seized on motorway and led to head gasket blowing and head crack. So, damn. Was working fine up until then.

Gave it to an engine rebuild specialist who restored the engine but on day 1 of picking it up from them car didn't feel like a peppy MR2 and cut out at every stop. Idle would drop to 500RPM, try to recover and then stutter low enough to cut out.

Took it right back. They said it was just a sticky throttle. Easy fix. Took to my normal mechanic for a throttle clean. Not the issue. Checked the entire electrical system. Rebuilt the ECU as it had some corrosion. Nothing else found electrically. Fuel pump apparently working as expected too. Usual mechanic says to take it back to engine place as they suspect the timing is the issue.

Took it back. Indeed they had put the cam belt back incorrectly and they fixed this a retimed it. Picked it up on Friday after assurances all was well (again) and it was just a bad as when I gave it to them still!

They are taking it back again this week.

Arghhh! What do you think the issue us? Other than these daft mechanics?

[mknz]

I would start with what's been changed while the issue appeared, e.g. it's unlikely a capacitor has popped in the ECU at the same time.

It sounds like between the engine being removed, disassmebled, and reassembled, some mistake has been made.

It's a bit hard to gauge what without a bit more information; how does it sound different? rough? at different RPM? at different load? how does it start up, any different? Does it run richer, leaner? How does it smell? etc. What parts were swapped or changed during the rebuild? It shouldn't smoke nor steam anymore. It's not overheating anymore? There's plenty of coolant in the filler neck? The temperature gauge reads normally?

There's three components in ICE; fuel, spark, air. It's one of these being out of wack. To be systematic it's worth keeping a list of things it could be, ordering them by percieved likelihood, going top to bottom. Take note of everything you learn along the way, it's easy to forget.

Air; it's probably one of these if it's stalling at idle. Either too much or too little fresh air is in the mix.
- There should be no obstructions obviously, no left behind rags
- There should be no vaccum leaks, it's also pretty easy to accidentally misconnect them. https://toyota.epc-data.com/mr2/sw20/15 ... /17341D/#1
- The mechanical timing should be right, the cam gears have a dot which should line up with a dash on the cover while the crank lines up with the TDC mark
- The ECU may think the engine is hotter than it actually is with air bubbles in the system and lowers the idle too quickly. The system should have bleed with the two bleed valves open, the rear at least level but preferably raised, and the heater on full hot. There should be a full filler cap with no little bubble appearing when it's warmed up.
- The throttle body should move freely without getting stuck from fully closed to fully open.
- The ACIS system (valves on the intake side to close half the ports for air velocity) should be closed at idle, it's controlled by vaccum and the ECU controlling the vaccum with a switching valve. This was probably only disconnected and reconnected.
- The idle air control valve shouldn't be getting stuck, probably not even touched, but should be connected
- The MAF sensor shouldn't have been touched and just connected back up again.
- The right cams should be in the head (surely they did this right)
- the valves should close properly, the clearances should (this would have to be seriously out of whack)

Spark; it's either weak, not at the right time, or in the wrong place.
- Spark plugs should be; BKR6EP-11 or PK20R8 or equivalent from a different manufacturer
- If you pull them out, and pull out the fuel pump fuse (or relay) there should be a nice strong spark, you can ground them to the rocker cover. If it's weak it could be the leads, it could be the distributor cap, it could be the rotor, it could be the coil. All but the coil could have been changed during the rebuild.
- The firing order is 1-3-4-2, the leads should match this. Cylinder 1 is timing belt side.
- The timing can be checked by bridging TE1 and E1 in the diagnostics connector and looking down at the timing marks with a timing light on it. It should be at 10 degrees BTDC (the mark below the 10). Use some white paint marker or twink to make it easier to see.

Fuel; well provided there's plenty of pressure, the injectors are the same, the rest of system hasn't been touched. It's probably not this. You can check this by disconnecting the return side of the rail which is below the oil fill cap and bridging the FP and +B pins (two rear most corner) on the diagnostic connector (little grey capped connector on the wall with the boot). It should be 30-40psi. I would check this last.

You may be frustrated with them, and don't let them charge you more, but keep it civil with them while keeping the pressure on to fix the problem. It's your best shot of getting this resolved.

[kilgh]

Awesome reply. Thank you.

I have owned this car for 16 years and never had this kind of frustration. I have another one also that is doing fine (although it's ECU blew and I had to get that rebuilt last year too).

So, they didn't take the engine out apparently to repair the head. But the fact that the car was running BETTER with a cracked head and blown gasket, idle wise, before they fixed it does indeed suggest it is something they have not re-connected properly. My regular mechanics sent it to an Electrical specialist to get their opinion and they have gone through all the possible electrical fault issues it could be and cleared it. So, unless THEY missed something it seems it isn't electrical.

The Engine specialists got the cam belt wrong so who knows what else they missed? I am being very polite with them as they are not taking any money from me so far to investigate. I just can't believe they keep returning it to me saying they took it for a test drive and it was "fine". I can only think that the issue maybe crops up while the engine is cold?

It starts fine, it sounds okay, it is just a really flat response at low speeds (completely unlike an MR2) and can't keep running when you come to a stop. So it feels like to me the fuel is too lean/not flowing well or there is air getting in somewhere it shouldn't maybe. All the sensors that the ECU read are coming back as responsive, but I guess that doesn't rule out they are sending faulty readings.

The throttle control has been checked by three different mechanics now and they all cleared it.

No signs of overheating. But, then I haven't taken it far enough to heat up fully as it is a pain to drive.

Alternator is quite new and seems to be charging fine (until the revs hit below 500rpm of course).

Frustrating.

But I will take your list here of things I hadn't thought of and subtly suggest some of them.

[85AW20v]

Maybe take your other MR2 - you have 2 if I read the post right - and show them what it should go like.....

[kilgh]

I was thinking of doing just that.

[Benckj]

Still sounds to me that they got timing wrong. I'll bet the intake cam is a tooth off which will throw the base timing by 6deg. Ask how they confirmed it was correct?

[kilgh]

Absolutely correct! It was a tooth off! However after fixing that they returned it to me "fixed" but the idling is JUST as bad.

[kilgh]

This was over a week ago and they promised to pick it up and have yet another go...but they haven't and haven't returned my call either. Having a shite week as I just got made redundant so really need this car working.