To expand on Pilgrim's suggestion, try disconnecting, cleaning (where possible) and reconnecting ALL electrical connectors under the hood at at the ECU, including injectors, fusible links, fuses and ESPECIALLY grounds where they bolt to the body.
Also, FWIW, most automotive shops these days don't know these cars, or how to correctly troubleshoot them. They will almost always suggest something that costs a lot of money. If I had a dime for every time I've read on this forum that "the shop said it was ABC so we replaced that and the problem was still there. So they said it was XYZ and we replaced that, but it still doesn't run right..."
The best way you can run down these problems (besides asking here) is to get a factory service manual and follow their troubleshooting guides. Also - again from years of learning the hard way - check the simple, stupid, cheap stuff first. These cars are extremely sensitive to good, tight electrical connections, good clean grounds, a full-power battery and charging system - and a good, tight vacuum system.
I can't tell you how many times I've replaced pricey stuff only to find that solution to the problem was one of those things that would have cost little or nothing to fix.